WO2019204515A1 - Circuits de lecture et procédés - Google Patents

Circuits de lecture et procédés Download PDF

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Publication number
WO2019204515A1
WO2019204515A1 PCT/US2019/027982 US2019027982W WO2019204515A1 WO 2019204515 A1 WO2019204515 A1 WO 2019204515A1 US 2019027982 W US2019027982 W US 2019027982W WO 2019204515 A1 WO2019204515 A1 WO 2019204515A1
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WO
WIPO (PCT)
Prior art keywords
sensor
readout
current
voltage
active
Prior art date
Application number
PCT/US2019/027982
Other languages
English (en)
Other versions
WO2019204515A4 (fr
Inventor
Edward Chan
Bing Wen
John Hong
Tallis Chang
Seung-Tak Ryu
Original Assignee
Obsidian Sensors, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Obsidian Sensors, Inc. filed Critical Obsidian Sensors, Inc.
Priority to US17/048,046 priority Critical patent/US11555744B2/en
Priority to EP24179836.2A priority patent/EP4403892A3/fr
Priority to CN202410401813.5A priority patent/CN118400626A/zh
Priority to EP19721942.1A priority patent/EP3782360B1/fr
Priority to KR1020207032970A priority patent/KR20200142575A/ko
Priority to CN201980031781.1A priority patent/CN112106349B/zh
Priority to JP2020557302A priority patent/JP7289851B2/ja
Publication of WO2019204515A1 publication Critical patent/WO2019204515A1/fr
Publication of WO2019204515A4 publication Critical patent/WO2019204515A4/fr
Priority to US18/097,138 priority patent/US20230236067A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
    • G01J5/20—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
    • G01J5/22—Electrical features thereof
    • G01J5/24—Use of specially adapted circuits, e.g. bridge circuits
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/4228—Photometry, e.g. photographic exposure meter using electric radiation detectors arrangements with two or more detectors, e.g. for sensitivity compensation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits
    • G01J1/46—Electric circuits using a capacitor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G01J5/02—Constructional details
    • G01J5/0225—Shape of the cavity itself or of elements contained in or suspended over the cavity
    • G01J5/024—Special manufacturing steps or sacrificial layers or layer structures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G01J5/02—Constructional details
    • G01J5/026—Control of working procedures of a pyrometer, other than calibration; Bandwidth calculation; Gain control
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G01J5/80—Calibration
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/20—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from infrared radiation only
    • H04N23/23—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from infrared radiation only from thermal infrared radiation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/30—Transforming light or analogous information into electric information
    • H04N5/33—Transforming infrared radiation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits
    • G01J2001/444—Compensating; Calibrating, e.g. dark current, temperature drift, noise reduction or baseline correction; Adjusting

Definitions

  • This disclosure generally relates to MEMS sensors. More specifically, this disclosure relates to sensor readout circuits, calibration circuits, and methods corresponding to the circuits.
  • a MEMS sensor array can convert a sensor image into a plurality of individual pixel signals.
  • a bolometer for example, an array of bolometer pixels are exposed to a thermal image (e.g., a spectrum of waves in the Long Wavelength Infrared range, hereinafter “LWIR”).
  • LWIR Long Wavelength Infrared range
  • Bolometer interference can be overwhelming.
  • Bolometer interference can manifest as large ambient interferences common to all the pixels in the array that arises from changes in the ambient condition and from self-heating of resistive elements (e.g., resistors in the circuit, the bolometer pixels themselves).
  • These common mode changes are typically large (e.g., up to +/- 50 K) compared to a minimum detectable thermal image signal on a given pixel (e.g., about 0.5 mK).
  • bolometer noise dominates the intended signal by many orders of magnitude.
  • Sensor noise can affect the clarity of a sensor image.
  • Noise in a bolometer array can include both temporal and spatially-patterned noise. Examples of noise include l/f noise, thermal noise, and process dependent variations.
  • noise include l/f noise, thermal noise, and process dependent variations.
  • sensor readout circuits include a reference sensor, an active sensor, current sources, a voltage driver, and a readout element.
  • methods include providing a current to a reference sensor, generating a common mode-tracking bias voltage electrically coupled to an active sensor, and measuring a current change at a readout element.
  • the disclosed circuits and methods reduce common mode effects without the cost and complexity of additional circuitry.
  • the circuits presented herein can efficiently and compactly track common mode changes in the sensor array.
  • accuracy of the measured thermal image signal can be improved, and the input range requirement of subsequent analog-to-digital converters (ADC) can be reduced without additional components for compensation.
  • ADC analog-to-digital converters
  • a sensor readout circuit includes a readout element, a first current source, a second current source, a voltage driver, a reference sensor, and an active sensor.
  • the readout element includes an input.
  • the voltage driver includes an output.
  • the reference sensor includes a first terminal and a second terminal; the first terminal is electrically coupled to the first current source and the second terminal is electrically coupled to the output of the voltage driver.
  • the active sensor includes a first terminal and a second terminal; the first terminal is electrically coupled to the second current source and the input of the readout element and the second terminal is electrically coupled to the output of the voltage driver.
  • the active sensor is configured for exposure to a sensor image.
  • the first current source and the second current source are constant sources.
  • the voltage driver generates a bias voltage for the active sensor.
  • the active sensor is further configured to change a current from the first terminal of the active sensor to the input of the readout element when the active sensor is exposed to the sensor image.
  • the active sensor is further configured to change an impedance of the active sensor when the active sensor is exposed to the sensor image.
  • the reference sensor is a reference bolometer pixel and the active sensor is an active bolometer pixel.
  • the circuit further includes a second reference sensor, a second active sensor, a first switch, a second switch, a third switch, and a fourth switch.
  • the second reference sensor includes a first terminal and a second terminal; the first terminal is electrically coupled to the first current source and the second terminal is electrically coupled to the voltage driver.
  • the second active sensor includes a first terminal and a second terminal; the first terminal is electrically coupled to the second current source outputting the second current and the second terminal is electrically coupled to the output of the voltage driver.
  • the second active sensor is configured to change the current from the first terminal to the input of the readout element.
  • the first switch is configured to selectively electrically couple the reference sensor to the first current source.
  • the second switch is configured to selectively electrically couple the active sensor to the second source.
  • the third switch is configured to selectively electrically couple the second reference sensor to the first current source.
  • the fourth switch is configured to selectively electrically couple the second active sensor to the second current source.
  • the circuit further includes a correlated double sampling (CDS) circuit that is configured to remove an offset.
  • CDS correlated double sampling
  • the voltage of the readout element is proportional to an impedance difference between the reference sensor and the active sensor.
  • the circuit further includes an output of an op amp electrically coupled to the second terminal of the reference sensor. [0019] In some embodiments, the circuit further includes a feedback element that is electrically coupled to the first and second terminals of the reference sensor.
  • the circuit further includes a third reference sensor and a third current source.
  • the third reference sensor includes a first terminal and a second terminal that is electrically coupled to the output of the voltage driver.
  • the third current source is electrically coupled to the first terminal of the third reference sensor, and is configured to output a seventh current reflective of self-heating generated by the third reference sensor. The value of the second current adjusts in accordance with the seventh current.
  • the circuit further includes an ADC that is configured to sample the change of the current from the first terminal to the input of the readout element.
  • the first current source and the second current source are configured to output an equal magnitude of current in a same direction relative to the respective first terminals.
  • the readout element includes a capacitive transimpedance amplifier (CTIA).
  • CTIA capacitive transimpedance amplifier
  • the first current source and the second current source are selected from the group of an athermal voltage source and resistor, a high-impedance athermal transistor current source, and a Wilson current mirror.
  • non-sensor elements of the readout circuit are designed to be substantively athermal and/or minimize the effects of self-heating.
  • the circuit further includes an amplifier that outputs to the second terminal of the reference sensor.
  • the first terminal of the reference sensor electrically couples to a negative input of the amplifier.
  • the first current source is configured to generate a voltage drop across the negative input and the output.
  • the reference sensor is a reference bolometer pixel
  • the active sensor is a bolometer pixel configured to detect LWIR radiation.
  • the readout element includes a Sigma-Delta ADC.
  • a first stage of the Sigma-Delta ADC includes a CTIA.
  • the reference sensor is shielded from a sensor image.
  • the circuit further includes a voltage follower electrically coupled between the output of the voltage driver and the second terminal of the active sensor.
  • the circuit further includes two or more current buffers, the two or more current buffers including a first current buffer electrically coupled between the first current source and the reference sensor and a second current buffer electrically coupled between the second current source and the active sensor.
  • the circuit further includes a fifth switch configured to selectively electrically couple the active sensor to the voltage driver.
  • a method of sensor readout includes: providing a first current to a first terminal of a reference sensor; generating, from the first current, a voltage at a second terminal of the reference sensor; providing a second current to a first terminal of an active sensor; driving, at the voltage, a second terminal of the active sensor; exposing the active sensor to a sensor image; and measuring a third current from the first terminal of the active sensor to an input of a readout element.
  • the first current and the second current are constant.
  • the voltage is a bias voltage for the active sensor.
  • exposing the active sensor to the sensor image further includes changing the third current.
  • exposing the active sensor to the sensor image further includes changing an impedance of the active sensor.
  • the method further includes: providing a fourth current to a first terminal of a second reference sensor; generating, from the fourth current, a second voltage at a second terminal of the second reference sensor; providing a fifth current to a first terminal of a second active sensor; driving, at the second voltage, a second terminal of the second active sensor; exposing the second active sensor to the sensor image; and measuring a sixth current from the first terminal of the second active sensor to the input of a readout element.
  • the method further includes: electrically uncoupling, from the reference sensor, a first current source providing the first current; coupling, to the second reference sensor, the first current source providing the fourth current; electrically uncoupling, from the active sensor, a second current source providing the second current; and coupling, to the second active sensor, the second current source providing the fifth current.
  • the method further includes: determining an offset generated by the input of the readout element; and canceling the offset prior to measuring the current to the input of the readout element.
  • a voltage at an output of the readout element is
  • the voltage is driven by an op amp, and the first terminal of the reference sensor is electrically coupled to a negative input of the op amp.
  • the method further includes feeding back from the second terminal of the reference sensor to the first terminal of the reference sensor.
  • the method further includes: providing a seventh current to a first terminal of a third reference sensor, the seventh current reflective of self-heating generated by the third reference sensor; and adjusting a value of the second current in accordance with the seventh current.
  • the method further includes sampling a voltage generated by the current to the input of a readout element.
  • the first current and the second current are equal in magnitude and in a same direction relative to the respective first terminals of the reference sensor and active sensor.
  • the method further includes converting the third current to a readout voltage of the readout element.
  • providing the first current and providing the second current each includes providing at least one selected from the group of an athermal voltage source and resistor, a high-impedance athermal transistor current source, and a Wilson current mirror.
  • driving the second terminal of the active sensor at the voltage further includes driving, from an output of a voltage driver, the second terminal of the reference sensor and the second terminal of the active sensor.
  • the method further includes causing a voltage drop across the reference sensor from the first current; generating the voltage using an amplifier outputting to the second terminal of the reference sensor; and electrically coupling the first terminal of the reference sensor to a negative terminal of the amplifier.
  • the reference sensor is a reference bolometer pixel and the active sensor is an active bolometer pixel.
  • exposing the active sensor to the sensor image further includes exposing the active sensor to LWIR radiation.
  • the readout element includes a Sigma-Delta ADC.
  • a first stage of the Sigma-Delta ADC includes a CTIA.
  • the method further includes exposing the reference sensor to an ambient condition common to the reference sensor and the active sensor; and shielding the reference sensor from the sensor image.
  • driving the second terminal of the active sensor at the voltage further includes buffering between the second terminal of the active sensor and a voltage source providing the voltage.
  • the method further includes: buffering the first current; and buffering the second current.
  • a method of manufacturing a sensor readout circuit includes providing a readout element including an input; providing a first current source; providing a second current source; providing a voltage driver including an output; providing a reference sensor including a first terminal and a second terminal; electrically coupling the first terminal of the reference sensor to the first current source; electrically coupling the second terminal of the reference sensor to the output of the voltage driver; providing an active sensor including a first terminal and a second terminal, the active sensor configured for exposure to a sensor image; electrically coupling the first terminal of the active sensor to the second current source and the input of the readout element; and electrically coupling the second terminal of the active sensor to the output of the voltage driver.
  • the first current and the second current sources are constant current sources.
  • the voltage driver is configured to generate a bias voltage for the active sensor.
  • the active sensor is further configured to change a current from the first terminal of the active sensor to the input of the readout element when the active sensor is exposed to the sensor image.
  • the active sensor is further configured to change an impedance of the active sensor when the active sensor is exposed to the sensor image.
  • the reference sensor is a reference bolometer pixel and the active sensor is an active bolometer pixel.
  • the method of manufacturing further includes: providing a second reference sensor including a first terminal and a second terminal; electrically coupling the first terminal of the second reference sensor to the first current source; electrically coupling the second terminal of the second reference sensor to the voltage driver; providing a second active sensor including a first terminal and a second terminal, the second active sensor configured for exposure to the sensor image; electrically coupling the first terminal of the active sensor to the second current source; electrically coupling the second terminal of the active sensor to the output of the voltage driver, and the second active sensor is configured to change a current from the first terminal of the active sensor to the input of the readout element; and providing a first switch configured to selectively electrically couple the reference sensor to the first current source; providing a second switch configured to selectively electrically couple the active sensor to the second current source; providing a third switch configured to selectively electrically couple the second reference sensor to the first current source; and providing a fourth switch configured to selectively electrically couple the second active sensor to the second current source.
  • the method of manufacturing further includes providing a CDS circuit configured to remove an offset.
  • the readout element is configured to generate a voltage proportional to an impedance difference between the reference sensor and the active sensor.
  • the method of manufacturing further includes: providing an op amp; and electrically coupling an output of an op amp to the second terminal of the reference sensor. [0069] In some embodiments, the method of manufacturing further includes: providing a feedback element; and electrically coupling the feedback element to the first and second terminals of the reference sensor.
  • the method of manufacturing further includes: providing a third reference sensor including a first terminal and a second terminal; electrically coupling the second terminal of the third reference sensor to the output of the voltage driver; providing a third current source configured to output a seventh current reflective of self-heating generated by the third reference sensor, and a value of the second current adjusts in accordance with the seventh current; and electrically coupling the third current source to the first terminal of the third reference sensor.
  • the method of manufacturing further includes providing an ADC configured to sample the change of the current from the first terminal to the input of the readout element.
  • the first current source and the second current source are configured to output an equal magnitude of current in a same direction relative to the respective first terminals.
  • the readout element includes a CTIA.
  • the first current source and the second current source are selected from the group of an athermal voltage source and resistor, a high-impedance athermal transistor current source, and a Wilson current mirror.
  • the method of manufacturing further includes: providing an amplifier outputting to the second terminal of the reference sensor; and electrically coupling the first terminal of the reference sensor to a negative input of the amplifier, the first current source configured to generate a voltage drop across the negative input and the output.
  • the reference sensor is a reference bolometer pixel and the active sensor is a bolometer pixel configured to detect LWIR radiation.
  • the readout element includes a Sigma-Delta ADC.
  • a first stage of the Sigma-Delta ADC includes a CTIA.
  • the reference sensor is shielded from a sensor image.
  • the method of manufacturing further includes: providing a voltage follower; and electrically coupling the voltage follower between the output of the voltage driver and the second terminal of the active sensor.
  • the method of manufacturing further includes: providing two or more current buffers including a first current buffer and a second current buffer;
  • the methods include measuring a voltage of the calibration sensor and computing a calibrated readout voltage based on the measured calibration sensor voltage. In some embodiments, the methods include measuring a readout voltage of a readout element electrically coupled to the calibration current source and computing an output based on the readout voltage caused by the calibration current. In some embodiments, the methods include measuring readout voltages when the shutter is closed and when the shutter is opened and computing a difference between the readout voltages.
  • row-to-row pattern noises can be caused by noise in the bias voltage, which can be common for a row of sensors. Therefore, the noise of the bias voltage is observed for an entire row of sensors.
  • column-to-column pattern noises can be caused by mismatch and l/f noise of skimming currents and ADC associated with specific columns of sensors.
  • the senor calibration circuits include a calibration sensor and a calibration readout element.
  • the sensor calibration circuits include a calibration current source.
  • a shutter is included with the sensor calibration circuits.
  • the disclosed circuits and methods remove noise at reduced costs.
  • the circuits presented herein efficiently and compactly remove noises in the sensor array.
  • the clarity of measured sensor images can be improved.
  • a sensor circuit includes: a plurality of active sensors exposed to a sensor image and sharing a bias voltage node; a calibration readout element; and a calibration sensor shielded from the sensor image and including a first terminal electrically coupled to the bias voltage node and a second terminal electrically coupled to the calibration readout element.
  • an impedance of the calibration sensor is the same as an impedance of an active sensor of the plurality of active sensors, and an electrical carrier count of the calibration sensor is greater than an electrical carrier count of the active sensor.
  • the sensor circuit further includes: a readout element corresponding to an active sensor of the plurality of active sensors and configured to measure a readout voltage of the active sensor, the calibration readout element is configured to measure a readout voltage of the calibration sensor, and the sensor circuit is electrically coupled to: a processor; and a memory including instructions, which when executed by the processor, cause the processor to perform a method that includes: receiving the readout voltage of the active sensor; receiving the readout voltage of the calibration sensor; and computing a difference between (1) the readout voltage of the active sensor and (2) the readout voltage of the calibration sensor weighted by a ratio between an impedance of the calibration sensor and an impedance of the active sensor.
  • the ratio is one.
  • the ratio is temperature independent.
  • the sensor circuit further includes: a readout element corresponding to an active sensor of the plurality of active sensors and configured to measure a readout voltage of the active sensor, the sensor circuit is electrically coupled to a processor and a memory including instructions, which when executed by the processor, cause the one or more processors to perform a method that includes: receiving a first readout voltage corresponding to a closed shutter; receiving a second readout voltage corresponding to an opened shutter; and computing a difference proportional to an impedance difference of the active sensor caused by the sensor image between (1) the first readout voltage and (2) the second readout voltage.
  • the plurality of readout elements includes a plurality of ADCs.
  • the calibration sensor and the plurality of active sensors are made from materials having a same thermal coefficient of resistance (TCR).
  • the plurality of active sensors includes a plurality of columns of active sensors, the circuit further includes: a plurality of current sources, a current source of the plurality of current sources is electrically coupled to the second terminal of the calibration sensor and the calibration readout element; and a plurality of readout elements, each of the plurality of columns of active sensors is electrically coupled to: a corresponding current source of the plurality of current sources at a corresponding readout node, and a corresponding readout element of the plurality of readout elements at the corresponding readout node.
  • the calibration readout element includes an analog-to- digital converter (ADC).
  • ADC analog-to- digital converter
  • the plurality of active sensors and the calibration sensor are bolometers, and the sensor image is a thermal image.
  • a sensor circuit includes: a calibration current source providing a calibration current; an active sensor; a readout element; a first switch configured to selectively electrically couple the active sensor to the readout element; and a second switch configured to selectively electrically couple the calibration current source to the readout element.
  • the second switch is configured to electrically uncouple the calibration current source from the first readout element when the first switch electrically couples the active sensor to the readout element
  • the first switch is configured to electrically uncouple the active sensor from the first readout element when the second switch electrically couples the calibration current to the readout element
  • the sensor circuit is electrically coupled to: a processor; and a memory including instructions, which when executed by the processor, cause the processor to perform a method including: receiving a first readout voltage of the active sensor; receiving a second readout voltage caused by the calibration current; and computing an output proportional to a readout current of the active sensor based on (1) the first readout voltage and (2) the second readout voltage.
  • the sensor circuit further includes: a plurality of active sensors including the active sensor; and a plurality of readout elements including the first and second readout elements, each of the plurality of readout elements electrically coupled to a respective active sensor of the plurality of active sensors, the method further includes:
  • the sensor circuit further includes a second active sensor belonging to a same column as the first active sensor
  • the method further includes, after computing the first output: receiving a third readout voltage of the second active sensor; and computing a second output proportional to a readout current of the fourth active sensor based on (1) the third readout voltage and (2) the second readout voltage caused by the calibration current.
  • a time between successive receipts of the second readout voltage on the same column caused by the calibration current is a calibration period.
  • the calibration period is one second.
  • the calibration period is based on a drift of the readout element.
  • different rows are readout during the successive receipts of the second readout voltage.
  • the sensor circuit further includes: a second calibration current source; a third switch configured to selectively electrically couple the first calibration current source to the readout element; and a fourth switch configured to selectively electrically couple the second calibration current source to the readout element, and when the third switch electrically uncouples the readout element from the first calibration current source: the fourth switch is configured to electrically couple the readout element to the second calibration current source, and the method further includes receiving a third readout voltage caused by the second calibration current; and the output is further based on the third readout voltage caused by the second calibration current.
  • the readout element includes an ADC.
  • the sensor circuit is electrically coupled to: a processor; and a memory including instructions, which when executed by the processor, cause the one or more processors to perform a method that includes: receiving a first readout voltage corresponding to a closed shutter; receiving a second readout voltage corresponding to an opened shutter; and computing a difference proportional to an impedance difference of the first active sensor caused by a sensor image between (1) the first readout voltage and (2) the second readout voltage.
  • the active sensor is a bolometer exposed to a thermal scene.
  • the active sensor is exposed to a sensor image and shares a bias voltage node with a plurality of active sensors
  • the sensor circuit further includes: a second readout element; and a calibration sensor shielded from the sensor image and including a first terminal electrically coupled to the bias voltage node and a second terminal electrically coupled to the second readout element.
  • Some embodiments include a method of manufacturing the above circuits.
  • a method of calculating a calibrated voltage in a sensor circuit includes: electrically coupling a first terminal of a calibration sensor to a bias voltage node shared by a plurality of active sensors; electrically coupling a second terminal of the calibration sensor to a calibration readout element; exposing the plurality of active sensors to a sensor image; shielding the calibration sensor from the sensor image; measuring, with a readout element, a readout voltage of an active sensor of the plurality of active sensors; measuring, with the calibration readout element, a readout voltage of the calibration sensor; and computing the calibrated voltage as a difference between (1) the readout voltage of the active sensor and (2) the readout voltage of the calibration sensor weighted by a ratio between an impedance of the calibration sensor and an impedance of the active sensor.
  • the impedance of the calibration sensor is the same as the impedance of the active sensor, and an electrical carrier count of the calibration sensor is greater than an electrical carrier count of the active sensor.
  • the ratio is one.
  • the ratio is temperature independent.
  • the calibration sensor and the active sensor are made from materials having a same TCR.
  • the method further includes: electrically coupling a current source of a plurality of current sources to the second terminal of the calibration sensor and to the calibration readout element; electrically coupling a column of a plurality of columns of active sensors to the readout element, the column of active sensors including the active sensor; and electrically coupling a second current source of the plurality of current sources to the readout element.
  • the method further includes: closing a shutter; measuring, with the readout element, a first readout voltage corresponding to the closed shutter; and measuring, with the calibration readout element, a second readout voltage corresponding to the closed shutter; and after computing the calibrated voltage, computing a second difference between (1) the calibrated voltage and a difference between (2a) the first readout voltage and (2b) the second readout voltage weighted by the ratio, the second difference is a shutter calibrated voltage.
  • the calibration readout element includes an ADC.
  • the readout element includes an ADC.
  • the plurality of active sensors and the calibration sensor are bolometers, and the sensor image is a thermal image.
  • a method of calculating an output in a sensor circuit includes: electrically coupling a readout element to an active sensor; measuring, with the readout element, a first readout voltage of the active sensor; electrically uncoupling the readout element from the active sensor; electrically coupling a calibration current to the readout element; measuring, with the readout element, a second readout voltage caused by the calibration current; and computing the output based on (1) the first readout voltage and (2) the second readout voltage, the output proportional to a readout current of the active sensor.
  • the method further includes: electrically coupling a respective active sensor of a plurality of active sensors to a readout element of a plurality of readout elements; measuring, with the respective readout element, a first readout voltage of the respective active sensor; electrically uncoupling the respective readout element from the respective active sensor; electrically coupling the calibration current to the respective readout element; measuring, with the respective readout element, a second readout voltage caused by the calibration current on the respective readout element; and computing an output proportional to a readout current of the respective active sensor based on (1) the first readout voltage of the respective active sensor and (2) the second readout voltage caused by the calibration current.
  • the method further includes, after computing the first output: electrically uncoupling the calibration current source from the readout element;
  • the readout element electrically coupling the readout element to a second active sensor, the second active sensor belonging to a same column as the first active sensor; measuring, with the readout element, a third readout voltage of the second active sensor; and computing a second output proportional to a readout current of the second active sensor based on (1) the third readout voltage and (2) the second readout voltage caused by the calibration current.
  • a time between successive measurements of the second readout voltage on the same column caused by the calibration current is a calibration period.
  • the calibration period is one second.
  • the calibration period is based on a drift of the readout element.
  • different rows are readout during the successive measurements of the second readout voltage.
  • the method further includes: electrically uncoupling the readout element from the first calibration current source; electrically coupling the readout element to a second calibration current source; and measuring, with the readout element, a third readout voltage caused by the second calibration current on the readout element, the output is further based on the third readout voltage caused by the second calibration current.
  • the readout element includes an ADC.
  • the method further includes: closing a shutter; computing the output corresponding to a closed shutter; and computing a difference proportional to an impedance difference of the active sensor caused by a sensor image between (1) the output corresponding to an opened shutter and (2) the output corresponding to the closed shutter.
  • the active sensor is a bolometer exposed to a thermal scene.
  • the method further includes: electrically uncoupling the readout element from the calibration current source; electrically coupling a second readout element to the calibration current source; measuring, with the second readout element, a third readout voltage caused by the calibration current; electrically uncoupling the second readout element from the calibration current source; electrically coupling a first terminal of a calibration sensor to a bias voltage node shared by a plurality of active sensors and the active sensor; electrically coupling a second terminal of the calibration sensor to the second readout element; exposing the plurality of active sensors and the active sensor to a sensor image; shielding the calibration sensor from the sensor image; measuring, with the second readout element, a fourth readout voltage of the calibration sensor; computing a second output based on the third readout voltage and the fourth readout voltage; and computing a difference between (1) the first output and (2) the second output weighted by a ratio between an impedance of the calibration sensor and an impedance of the active sensor.
  • the senor circuit includes a plurality of sensor pixels, a Sigma-Delta ADC, and a plurality of switches.
  • the sensor circuit includes columns of sensors, and different parts of a column of sensors are being read out at a same time.
  • a sensor circuit includes: a plurality of sensor pixels, each configured to store a charge; a Sigma-Delta ADC configured to receive the charge of each sensor; and a plurality of switches configured to sequentially couple each of the plurality of sensor pixels to the Sigma-Delta ADC, each switch corresponding to a respective one of the plurality of sensor pixels.
  • the sensor circuit does not include a CTIA electrically positioned between the plurality of sensor pixels and the Sigma-Delta ADC.
  • the sensor circuit further includes a variable resistor electrically positioned between the plurality of sensors and the Sigma-Delta ADC, wherein the plurality of switches are configured to sequentially couple each of the plurality of sensor pixels to the variable resistor.
  • variable resistor has a linearly decreasing resistance during a discharge time window; the variable resistor is at a lowest resistance at an end of the discharge time window; and the variable resistor has a resistance higher than the lowest resistance between the beginning and the end of the discharge time window.
  • the variable resistor is a MOS transistor; and the initial resistance, the linearly decreasing resistance, and the lowest resistance of the MOS transistor are controlled with a control voltage electrically coupled to the MOS transistor.
  • the discharge time window is between 10 microseconds and 1 millisecond.
  • a first switch electrically couples a first sensor pixel and the Sigma-Delta ADC; during a second discharge time window, a second switch electrically couples a second sensor pixel and the Sigma-Delta ADC; and the first and second discharge time windows correspond to readout times of the first and second sensor pixels.
  • a constant current of the variable resistor is an initial voltage of the variable resistor divided by the initial resistance.
  • a switch electrically couples a respective sensor pixel and the variable resistor during a respective discharge time window, the discharge time window equal to a capacitance of the sensor pixel multiplied by an initial resistance of the variable resistor.
  • variable resistor includes a weighted bank of resistors; the weighted bank of resistors include a plurality of resistors selectively electrically coupled in parallel or in series; and resistances of combinations of the selective electrically coupled resistors include an initial resistance at the beginning of a discharge time window, a linearly decreasing resistance, and a lowest resistance.
  • a sensor pixel includes an x-ray sensor photodiode and the charge is indicative of the x-ray sensor photodiode’s exposure to x-ray.
  • a sensor pixel includes a storage capacitor storing the charge and the sensor pixel’s exposure to x-ray generates the charge stored in the storage capacitor.
  • the sensor circuit further includes a second plurality of sensor pixels and a second Sigma-Delta ADC, wherein the second plurality of sensor pixels are configured to sequentially couple to the second Sigma-Delta ADC and the first and second pluralities of sensor pixels belong to a same column. [0147] In some embodiments, numbers of the first and second plurality of sensor pixels are equal.
  • a first sensor pixel of the first plurality of sensor pixels and a second sensor pixel of the second plurality of sensor pixels are simultaneously readout.
  • an input current to the Sigma-Delta ADC is constant.
  • the sensor circuit further includes a digital filter configured to receive a signal from the Sigma-Delta ADC.
  • Some embodiments include a method of manufacturing the above circuits.
  • a sensor circuit includes a plurality of sensor pixels, a Sigma-Delta ADC, and a plurality of switches, each switch corresponding to a respective one of the plurality of sensor pixels; a method of readout of the sensor circuit includes: storing respective charges in each of the plurality of sensor pixels; sequentially electrically coupling, using the plurality of switches, each of the plurality of sensor pixels to the Sigma-Delta ADC; and sequentially receiving, at the Sigma-Delta ADC, the respective charge of each sensor pixel.
  • the sensor circuit does not include a CTIA electrically positioned between the plurality of sensor pixels and the Sigma-Delta ADC and the respective charge of each sensor pixel is not received by the CTIA.
  • the sensor circuit further includes a variable resistor electrically positioned between the plurality of sensor pixels and the Sigma-Delta ADC and the method further includes sequentially electrically coupling, using the plurality of switches, each of the plurality of sensor pixels to the Sigma-Delta ADC further includes sequentially electrically coupling, using the plurality of switches, the each of the plurality of sensor pixels to the variable resistor.
  • the method further includes linearly decreasing a resistance of the variable resistor during a discharge time window, wherein: the variable resistor is at a lowest resistance at an end of the discharge time window; and the variable resistor has a resistance higher than the lowest resistance between the beginning and the end of the discharge time window.
  • the variable resistor is a MOS transistor electrically coupled to a control voltage and linearly decreasing the resistance of the variable resistor further includes driving the MOS transistor with the control voltage to generate the initial resistance, the linearly decreasing resistance, and the lowest resistance.
  • the discharge time window is between 10 microseconds and 1 millisecond.
  • sequentially electrically coupling, using the plurality of switches, each of the plurality of sensor pixels to the Sigma-Delta ADC further includes: during the first discharge time window, electrically coupling a first switch to a first sensor pixel and the Sigma-Delta ADC; during a second discharge time window, electrically coupling a second switch to a second sensor pixel and the Sigma-Delta ADC, wherein the first and second discharge time windows correspond to readout times of the first and second sensor pixels.
  • a constant current of the variable resistor is an initial voltage of the variable resistor divided by the initial resistance.
  • sequentially electrically coupling, using the plurality of switches, each of the plurality of sensor pixels to the Sigma-Delta ADC further includes electrically coupling a switch to a respective sensor pixel and the variable resistor during a respective discharge time window; and the discharge time window is equal to a capacitance of the sensor pixel multiplied by an initial resistance of the variable resistor.
  • the variable resistor includes a weighted bank of resistors; the weighted bank of resistors include a plurality of resistors selectively electrically coupled in parallel or in series; and the method further includes linearly decreasing resistances of combinations of the plurality of resistors, from an initial resistance at a beginning of a discharge time window to a lowest resistance at an end of the discharge time window, by selective electrically coupling the resistors.
  • a sensor pixel includes an x-ray sensor photodiode and the charge is indicative of the x-ray sensor photodiode’s exposure to x-ray.
  • storing respective charges in each of the plurality of sensor pixels further includes: exposing the each of the plurality of sensor pixels to x-ray and generating the respective charge; and storing the respective charges in a storage capacitor of the each of the plurality of sensor pixels.
  • the sensor circuit further includes a second plurality of sensor pixels belonging to a same column as the first plurality of sensor pixels, a second plurality of switches, and a second Sigma-Delta ADC, the method further includes:
  • each of the plurality of sensor pixels sequentially electrically coupling, using the second plurality of switches, each of the plurality of sensor pixels to the second Sigma-Delta ADC; and sequentially receiving, at the second Sigma-Delta ADC, the respective charge of each sensor pixel of the second plurality of sensor pixels.
  • numbers of the first and second plurality of sensor pixels are equal.
  • the first Sigma-Delta ADC receives a first respective charge of a first sensor pixel of the first plurality of sensor pixels; and the second Sigma-Delta ADC receives a second respective charge of a second sensor pixel of the second plurality of sensor pixels.
  • the Sigma-Delta ADC receives a constant current.
  • FIG. 1 illustrates a sensor readout circuit, in accordance with an embodiment.
  • FIG. 2 illustrates a method of sensor readout, in accordance with an embodiment.
  • FIG. 3 illustrates a sensor readout circuit, in accordance with an embodiment.
  • FIG. 4 illustrates a method of sensor readout, in accordance with an embodiment.
  • FIG. 5 illustrates a sensor readout circuit, in accordance with an embodiment.
  • FIG. 6 illustrates a sensor readout circuit, in accordance with an embodiment.
  • FIG. 7 illustrates a method of current adjustment, in accordance with an embodiment.
  • FIG. 8 illustrates a sensor bias circuit, in accordance with an embodiment.
  • FIG. 9 illustrates a sensor readout system, in accordance with an embodiment.
  • FIG. 10 illustrates a sensor readout circuit, in accordance with an embodiment.
  • FIG. 11 illustrates a sensor calibration circuit, in accordance with an embodiment.
  • FIG. 12 illustrates a method of sensor calibration according to examples of the disclosure.
  • FIG. 13 illustrates a sensor calibration circuit, in accordance with an embodiment.
  • FIG. 14 illustrates a method of sensor calibration, in accordance with an embodiment.
  • FIG. 15 illustrates a sensor calibration circuit, in accordance with an embodiment.
  • FIG. 16 illustrates a sensor calibration circuit, in accordance with an embodiment.
  • FIG. 17 illustrates a method of sensor calibration, in accordance with an embodiment.
  • FIGS. 18A and 18B illustrate exemplary sensor images, in accordance with an embodiment.
  • FIGS. 19A and 19B illustrate exemplary sensor circuits, in accordance with an embodiment.
  • FIGS. 20A and 20B illustrate exemplary sensor circuits, in accordance with an embodiment.
  • FIGS. 21A to 21D illustrate exemplary inputs, in accordance with an embodiment.
  • FIG. 22 illustrates a method of manufacturing MEMS products, in accordance with an embodiment.
  • FIG. 23 illustrates a bolometer, in accordance with an embodiment.
  • sensor readout circuits include a reference sensor, an active sensor, current sources, a voltage driver, and a readout element.
  • methods include providing a current to a reference sensor, generating a common mode-tracking bias voltage electrically coupled to an active sensor, and measuring a current change at a readout element.
  • the disclosed circuits and methods reduce common mode effects without the cost and complexity of additional circuitry.
  • the circuits presented herein can efficiently and compactly track common mode changes in the sensor array.
  • accuracy of the measured thermal image signal can be improved, and the input range requirement of subsequent analog-to-digital converters (ADC) can be reduced without additional components for compensation.
  • ADC analog-to-digital converters
  • FIG. 1 illustrates a sensor readout circuit 100, in accordance with an embodiment.
  • the sensor readout circuit 100 includes a readout element 102, a first current source 104, a second current source 106, a voltage driver 108, a reference sensor 110, and an active sensor 112.
  • Some embodiments include a method of manufacturing the readout circuit 100.
  • the readout element includes an input 103.
  • the voltage driver includes an output 109.
  • the reference sensor 110 includes a first terminal 1 lOa and a second terminal 1 lOb; the first terminal 1 lOa is electrically coupled to the first current source 104 and the second terminal 110b is electrically coupled to the output 109 of the voltage driver 108.
  • the active sensor 112 includes a first terminal 1 l2a and a second terminal 1 l2b; the first terminal 1 l2a is electrically coupled to the second current source 106 and the input 103 of the readout element 102; and the second terminal H2b is electrically coupled to the output 109 of the voltage driver 108.
  • the active sensor 112 is configured for exposure to a sensor image.
  • a voltage follower (not shown) can be electrically coupled between output 109 and second terminal 1 l2b.
  • a voltage follower may advantageously buffer the voltage at output 109 from effects of capacitive loading.
  • the simplified topology as exemplified in FIG. 1, requires one voltage driver, which provides a bias voltage. Without adding circuitry to reduce undesired common mode effects, the topology can reduce undesired common effects without increasing complexity, size, and cost, introducing more parasitics and unknowns, consuming more power, and adding noise inducing components.
  • the reference sensor 110 is shielded from the sensor image.
  • the reference sensor 110 can be exposed to an ambient condition common to the reference sensor and active sensor.
  • the reference sensor is a reference or blind bolometer pixel that is exposed to ambient temperatures, but is not exposed to a thermal scene
  • the active sensor is an active bolometer pixel, which is exposed to both the ambient temperatures and the thermal scene.
  • the sensors include two terminals and can have a variable impedance value between the two terminals that depends on a sensor image.
  • resistor and variable resistor symbols are used to represent the sensors in this disclosure, it is understood that sensor properties and components are not limited to resistive elements between two terminals.
  • bolometer is used to exemplify the disclosed sensors, it is understood that the term“bolometer” is not limited to a single pixel or a single device.
  • a bolometer can be any element that is configured to change an output characteristic in response to exposed radiation.
  • a bolometer can be one or more pixels.
  • a bolometer can be one more devices.
  • the term“bolometer pixel” is used to exemplify the disclosed sensors, it is understood that the disclosed sensors can include more than one bolometer pixel without departing from the scope of this disclosure.
  • the reference sensor 110 generates an adjustable bias voltage at output 109 that tracks both ambient conditions and self-heating.
  • the readout circuit operates in a constant current mode, compared to the constant voltage mode of other readout circuits.
  • a first current provided by the first current source 104 is constant. Since no other branch is connected between the first current source and the reference sensor, the current traversing the reference sensor is also constant at the value of the first current.
  • the impedance of the reference sensor stabilizes according to a value that is reflective of the exposed ambient conditions.
  • the impedance of the sensor is substantially fixed at a stable state, it is understood that the impedance of the reference sensor can vary according to the ambient conditions.
  • a voltage drop is generated between first terminal 1 lOa and second terminal 1 lOb due to the first current and the reference sensor impedance. Due to the voltage drop, the voltage at the second terminal 110b is generated by the difference between the voltage at the first terminal 1 lOa and the voltage drop across the two terminals.
  • the voltage at the second terminal 110b is driven by voltage driver 108 at output 109.
  • voltage driver 108 can act substantially as an ideal voltage source. In other words, the voltage driver 108 can provide (or absorb) the necessary current at output 109 to maintain the generated voltage at the second terminal 1 lOb.
  • voltage driver 108 The symbol illustrating voltage driver 108 is used for illustrative purposes only. It is apparent to a person of ordinary skill in the art that different methods and circuits can be utilized to drive the voltage at the second terminal 1 lOb. Although an input of the illustrative voltage driver 108 is shown as floating, it is understood that the input is merely representative and can be connected to a suitable element of the readout circuit to maintain the output voltage.
  • the voltage at the second terminal 1 lOb is significant because it is reflective of common mode effects, such as self-heating and ambient conditions, observed by the reference sensor 110.
  • the common mode effects (which can disadvantageously reduce the dynamic range of subsequent stages) have been effectively compensated because the biasing voltage is reflective of common mode conditions.
  • the sensor readout circuit 100 is symmetrically
  • active sensor 112 is substantially the same as reference sensor 110, and the second current source 106 can provide substantially the same current as the first current source 104.
  • the first current source and the second current source are configured to output an equal magnitude of current in a same direction relative to the respective first terminals.
  • currents provided by the first and second current sources can flow toward a reference potential 120.
  • the reference potential 120 is at a reference voltage. In another embodiment, the reference potential 120 is a ground.
  • input 103 of the readout element 102 can have a low input resistance, such as an input of a charge amplifier.
  • a low input resistance such as an input of a charge amplifier.
  • the reference and active sensors are exposed to substantially the same conditions, and the first and second current sources provide substantially the same currents, no current would enter or exit the input 103 because the current traversing the active sensor 112 would be the same as the current provided by the second current source 106.
  • An example of this condition is when the exposed sensor image is the ambient condition itself.
  • the reference and active sensors are exposed to different conditions (i.e.
  • a current would enter or exit the input 103 because the impedance of the active sensor 112 is different from the impedance of the reference sensor 110, and the values of the provided currents remain the same after exposure.
  • the current or total charge entering or exiting the input 103 is captured and measured in the readout element 102.
  • the disclosed circuits and methods remove common mode effects without the cost and complexity of additional circuitry.
  • the circuits presented herein efficiently and compactly track common mode changes in the sensor array. Thus, accuracy of the measured thermal image signal can be improved and the input range requirement of subsequent ADCs can be reduced without additional components for compensation.
  • the disclosed readout circuits and methods can tolerate greater variations of circuit elements. For example, since the common mode effects are removed, thermal dependency of the transistors and resistive components can be ignored.
  • an array of active sensors can be measured. Based on the captured or measured currents or charges, a sensor image can be computed. Exemplary methods and circuits performing the measurements and computations are discussed later in this disclosure.
  • the active sensors are active bolometer pixels exposed to a thermal scene
  • the reference sensors are blind or reference bolometer pixels that are exposed to ambient temperatures, but not the thermal scene.
  • the active bolometer pixel is exposed to LWIR radiation.
  • the reference bolometer pixel determines a bias voltage that compensates for common mode effects.
  • the impedance of the active bolometer pixel can change and the resulting change in current is measured or captured to determine the thermal image associated with the thermal scene. The measured current is compensated for common mode effects.
  • the first current and the second current provided by the current sources 104 and 106 are constant. For example, the current sources are athermal.
  • the values of the currents are substantially unaffected by temperature. Additionally or alternatively, the current sources can substantially act like an ideal current source. For example, a value of current provided by the current source is fixed regardless of an output voltage of the corresponding current source.
  • “constant current” means a current that is independent of other parameters (e.g., temperature, output voltage of a current source, driving load, driving speed).
  • the current can have a first fixed value during a readout time and have a second fixed value during a non readout period (e.g., calibration, sleep, low power, power off).
  • the current can have a third fixed value during a first readout time and have a fourth fixed value during a second readout time.
  • a first current buffer is coupled between the reference sensors and the first current source and a second current buffer is coupled between the active sensors and the input of the readout element.
  • the current buffers shield undesired effects at the input nodes (e.g., input of the readout element, an input of the voltage driver) from signals generated by the reference and active sensors. For example, undesired current can be injected into the input nodes and modulate the voltages at these nodes. The current buffers prevent the signal currents from being affected by the undesired injected currents.
  • the current source can be any one or more circuit elements that can provide a constant and/or athermal current.
  • the first current source and the second current source are one or more of an athermal voltage source and resistor, a high-impedance athermal transistor current source, and a Wilson current mirror.
  • the readout circuit is electrically coupled to a calibration circuit.
  • the calibration circuit includes one or more calibration current sources, one or more fourth reference sensors, and a calibration readout element.
  • the one or more calibration current sources are configured to provide one or more calibration currents to electrically coupled columns of active and reference sensors and the calibration readout element.
  • the calibration current sources are fixed current sources.
  • the one or more fourth reference sensors are electrically coupled to the bias voltage and the calibration readout element.
  • the calibration readout element is a calibration ADC.
  • each of the one or more fourth references is physically larger than a reference sensor of the readout circuit and has a same impedance as a reference sensor of the readout circuit. The physically larger fourth reference sensor is less noisy than a reference sensor of the readout circuit.
  • the readout element is an ADC; an ADC is associated with a column of active or reference sensors.
  • Non-idealities such as gain mismatches, noise, and/or offset of the ADC are calibrated in a calibration mode. In some examples, the non idealities cause undesired fixed patterns, distorting the sensor image.
  • the calibration mode during readout of each row, some or all the voltage driver and readout element inputs are electrically decoupled from the reference and active sensors of the readout circuit, respectively.
  • One or more calibration currents are electrically coupled to the voltage driver and readout element inputs that are electrically decoupled from the reference and active sensors of the readout circuit and the calibration readout element.
  • a measured value of the calibration readout element can be subtracted from one or more measured values of the readout element inputs electrically coupled to the one or more calibration currents.
  • the one or more calibration currents electrically couple to one or more different readout element inputs for each row readout period.
  • electrically coupled and“coupled” are used to describe the electrical connections between two elements of the readout circuit in this disclosure, it is understood that the electrical connections do not necessarily need direct connection between the terminals of the components being coupled together. Different combinations and connections of the recited components can achieve a constant current and adjustable bias voltage readout circuit without departing from the scope of this disclosure.
  • electrical routing connects between the terminals of the components being electrically coupled together.
  • a closed (conducting) switch is connected between the terminals of the components being coupled together.
  • additional elements connect between the terminals of the components being coupled together without affecting the constant current characteristics of the circuit. For example, buffers, amplifiers, and passive circuit elements can be added without affecting the characteristics of the readout circuit and departing from the scope of this disclosure.
  • two electrically coupled components may be topologically coupled.
  • two components are“topologically coupled” if they provide an electrical influence on one another within a topology or a same part of a topology.
  • the reference sensor and the first current source of the disclosed readout circuits are electrically coupled on a same reference branch of the readout circuit.
  • “electrically uncoupled” is used to describe electrical disconnects between two elements of the readout circuit in this disclosure, it is understood that electrical disconnects do not necessarily need to be physically open between the terminals of the components being switched. It is also understood that“uncoupled” is not limited to mean prevention of electrical energy transfer between two elements. For example, high-impedance elements are connected between the terminals of the components being uncoupled. In another example, an opened (non-conducting) switch is connected between the terminals of the components being uncoupled, effectively uncoupling the components.
  • FIG. 2 illustrates a method 200 of sensor readout, in accordance with an embodiment.
  • Method 200 includes providing a first current to a first terminal of a reference sensor (step 202).
  • a first current source 104 can provide a first current to the first terminal 1 lOa of the reference sensor 110.
  • Method 200 includes generating, from the first current, a voltage at a second terminal of the reference sensor (step 204). For example, due to the first current and the impedance of the reference sensor, a voltage drop across the reference sensor 110 and a voltage at the second terminal 110b are generated.
  • Method 200 includes providing a second current to a first terminal of the active sensor (step 206).
  • a second current source 106 can provide a second current to the first terminal 1 l2a of the active sensor 112.
  • the first current and the second current are constant.
  • the first current source and the second current source are configured to output an equal magnitude of current in a same direction relative to the respective first terminals. For example, currents provided by the first current source 104 and second current source 106 can flow toward a reference potential 120.
  • the reference potential 120 is a reference voltage driven by a voltage source. In another embodiment, the reference potential 120 is a ground.
  • the first current source and the second current source are selected from the group of an athermal voltage source and resistor, a high-impedance athermal transistor current source, and a Wilson current mirror.
  • Method 200 includes driving, at the voltage, a second terminal of an active sensor (step 208).
  • the second terminal 1 lOb of the reference sensor 110 is electrically coupled to the second terminal H2b of the active sensor 112, and the voltage at this node is driven by voltage driver 108 at output 109.
  • the voltage is a bias voltage for the active sensor.
  • the bias voltage is reflective of common mode effects. By biasing the active sensor at the voltage, these common mode effects can be compensated.
  • a voltage follower can be electrically coupled between output 109 and second terminal 1 l2b.
  • a voltage follower may advantageously buffer the voltage at output 109 from effects of capacitive loading.
  • Method 200 includes exposing the active sensor to a sensor image (step 210).
  • active sensor 112 is exposed to a sensor image.
  • exposing the active sensor to the sensor image further includes changing an impedance of the active sensor.
  • the active sensor is an active bolometer pixel.
  • the active bolometer pixel is exposed to a thermal scene.
  • the impedance of the active bolometer pixel can change in response to exposure to the thermal scene.
  • exposing the active sensor to the sensor image includes exposing the active sensor to LWIR radiation.
  • Method 200 includes measuring a third current from the first terminal of the active sensor to an input of a readout element (step 212). For example, a current entering or exiting input 103 of the readout element 102 is measured.
  • exposing the active sensor to the sensor image further includes changing the third current.
  • the active sensor is an active bolometer pixel.
  • the active bolometer pixel is exposed to a thermal scene.
  • a current entering or exiting input 103 of the readout element 102 can change.
  • method 200 further includes exposing the reference sensor to an ambient condition common to the reference sensor and active sensor; and shielding the reference sensor from the sensor image.
  • the sensor is a bolometer pixel and the common conditions are self-heating and ambient temperature.
  • the reference bolometer pixel is exposed to the common conditions, but is shielded from the thermal scene.
  • the reference sensor is a reference bolometer pixel and the active sensor is an active bolometer pixel.
  • the active sensor is an active bolometer pixel exposed to a thermal scene
  • the reference sensor is a blind or reference bolometer pixel that is exposed to ambient temperatures, but not the thermal scene.
  • the reference bolometer pixel can determine a bias voltage that compensates for common mode effects.
  • the impedance of the active bolometer pixel can change and the resulting change in current is measured or captured to determine the thermal image associated with the thermal scene. The measured current is compensated for common mode effects.
  • a first current buffer is coupled between the reference sensors and the first current source and a second current buffer is coupled between the active sensors and the input of the readout element.
  • the current buffers shield undesired effects at the input nodes (e.g., input of the readout element, an input of the voltage driver) from signals generated by the reference and active sensors. For example, undesired current can be injected into the input nodes and modulate the voltages at these nodes. The current buffers prevent the signal currents from being affected by the undesired injected currents.
  • FIG. 3 illustrates a sensor readout circuit, in accordance with an embodiment.
  • the readout circuit 300 includes components that are substantially similar to those described in FIG. 1.
  • FIG. 3 Like components in FIG. 3 are given like numerals as the corresponding components in FIG. 1 (for example, read out element 102 and read out element 302). For the sake of brevity, those like components are not described again with respect to FIG. 3. Some embodiments include a method of manufacturing the readout circuit 300.
  • Circuit 300 further includes a second reference sensor 320, a second active sensor 322, a first switch 330, a second switch 332, a third switch 334, a fourth switch 336, and a voltage follower 318.
  • the second reference sensor 320 includes a first terminal 320a and a second terminal 320b; the first terminal 320a is electrically coupled to the first current source 304 and the second terminal 320b is electrically coupled to output 309 of voltage driver 308.
  • the second active sensor 322 includes a first terminal 322a and a second terminal 322b; the first terminal 322a is electrically coupled to the second current source 306 outputting the second current and the second terminal 322b is electrically coupled to voltage follower 318.
  • the second active sensor 322 is configured to change the current from the first terminal 322 to the input 303 of the readout element 302.
  • a voltage follower 318 is electrically coupled between the output 309 and second terminal 3l2b of the active sensor 312.
  • the voltage follower 318 acts as a voltage buffer.
  • the voltage follower 318 can reduce the output loading of the voltage driver 308.
  • an active column includes more than one active sensor (this configuration discussed below).
  • the bias voltage is driven to more than one active column.
  • the loading (e.g., capacitive load) at the active bias voltage node increases as the size of the column and/or the number of columns being driven increases.
  • the voltage follower 318 can maintain the size of the voltage driver 308 and a desirable active bias voltage response.
  • a voltage follower 318 is illustrated as being electrically coupled between the voltage driver 308 and the active sensor 312, it is understood that the readout circuit 300 can include no voltage follower (e.g., the voltage driver 308 is electrically coupled to both second terminals 3l0b and 3l2b, providing the active bias voltage) or more than one voltage followers (e.g., multi-stage voltage buffers, parallel voltage followers) without departing from the scope of this disclosure.
  • the symbol illustrating voltage follower 318 is used for illustrative purposes only. It is apparent to a person of ordinary skill in the art that different methods and circuits can be utilized to drive the voltage at the second terminal 312b.
  • the first switch 330 is configured to selectively electrically couple the reference sensor 310 to the first current source 304.
  • the second switch 332 is configured to selectively electrically couple the active sensor 312 to the second current source 306.
  • the third switch 334 is configured to selectively electrically couple the second reference sensor 320 to the first current source 304.
  • the fourth switch is configured to selectively electrically couple the second active sensor 322 to the second current source 306.
  • the switches can be any suitable components that can selectively electrically couple the circuit elements.
  • the switches are transistors.
  • the switches can electrically couple to a controller that closes the appropriate switches based on a readout scheme.
  • the circuit 300 can be configured for readout operation of a sensor array including two or more rows.
  • the reference sensor 310 and the active sensor 312 are associated with a first row of the sensor array
  • the second reference sensor 320 and the second active sensor 322 are associated with a second row of the sensor array.
  • the first row is selected for readout.
  • the first switch 330 and the second switch 332 are closed (conducting), coupling the reference sensor 310 to the first current source 304 and the active sensor 312 to the second current source 306, respectively.
  • the third switch 334 and the fourth switch 336 are opened (not conducting), keeping the second reference and active sensors electrically uncoupled from their respective current sources.
  • the first switch 330 and the second switch 332 are open (not conducting), electrically uncoupling the reference sensor 310 to the first current source 304, and the active sensor 312 to the second current source 306, respectively.
  • the third switch 334 and the fourth switch 336 are closed (conducting), electrically coupling the second reference sensor 320 to the first current source 304 and the second active sensor 322 to the second current source 306, respectively.
  • the mechanism described in this disclosure can cause a current to enter or exit the input 303 of the readout element 302. Accordingly, the readout data of the currently selected active sensor can be subsequently processed. This process can be repeated for subsequent rows until the entire sensor array has been scanned or until the intended rows have been scanned.
  • row-to-row readout operation for an active sensor column is described, it is understood that the operation is not limited to one column.
  • the operation can be performed in sequence or simultaneously for one or more columns of active sensors using one or more columns of reference sensors.
  • switches are configured as illustrated, the switches can be suitably connected in different manners without departing from the scope of this disclosure.
  • additional switches are electrically coupled between the second terminals and the voltage follower or the bias voltage node.
  • a voltage follower may be supplemented with or replaced by additional switches electrically coupled between the second terminals and voltage driver.
  • the additional switches are coupled between the second terminals and the voltage driver, the second terminals of the one or more active sensors are not the same node in the circuit (with or without the voltage follower).
  • a respective additional switch of a selected row is closed (conducting) while the other additional switches of the non-selected rows are open (not conducting).
  • the loading at the second terminal of the selected active sensor is reduced because the loading of the second terminals of the non- selected active sensors are effectively removed.
  • the voltage driver 308 is an op amp.
  • the output 309 of the op amp 308 is electrically coupled to the second terminals of the reference sensors.
  • the negative input of the op amp can electrically couple to the first terminals of the reference sensors.
  • the selected reference sensor and the op amp can form an inverting amplifier.
  • the amplifier can output a bias voltage to the second terminals of the reference sensors.
  • the output bias voltage can be substantially the same as the bias voltage described elsewhere in this disclosure.
  • the first terminals of the reference sensors electrically couple to a negative input of the amplifier. Since the first current source 304 provides the first current to the first terminal, a voltage drop across the negative input and the output is generated, and an appropriate bias voltage is driven by the amplifier based on the voltage drop.
  • a reference voltage can electrically couple to the positive terminal of the op amp.
  • the reference voltage is a constant voltage or a ground voltage.
  • a feedback element 338 is electrically coupled to the first and second terminals of the reference sensor.
  • the feedback element can provide an additional negative feedback path for the op amp 308.
  • the feedback element is a capacitor.
  • the feedback element is a sensor substantially similar to the reference sensor.
  • the feedback element 338 can keep the feedback loop of the voltage driver closed during row transitions, thus preventing the voltage driver 308 from railing or saturating at an open loop situation.
  • the capacitor can be sized appropriately such that the voltage at output 309 will be the desired voltage at the start of the readout of the next row.
  • a first current buffer is coupled between the reference sensors and the first current source and a second current buffer is coupled between the active sensors and the input of the readout element.
  • the current buffers shield undesired effects at the input nodes (e.g., input of the readout element, negative terminal of voltage driver 308) from signals generated by the reference and active sensors.
  • undesired current can be injected into the input nodes and modulate the voltages at these nodes.
  • the current buffers prevent the signal currents from being affected by the undesired injected currents.
  • FIG. 4 illustrates a method 400 of sensor readout, in accordance with an embodiment.
  • method 400 is used in conjunction with method 200.
  • method 400 is performed using the readout circuits described in this disclosure.
  • Method 400 includes providing a fourth current to a first terminal of a second reference sensor (step 402).
  • a first current source 304 can provide a fourth current to the first terminal 320a of the second reference sensor 320.
  • the first current and the fourth current have the same magnitude.
  • Method 400 can further include electrically uncoupling, from the reference sensor, the first current source providing the first current; and coupling, to the second reference sensor, the first current source providing the fourth current.
  • the first switch 330 can open (not conduct), electrically uncoupling the reference sensor 310 to the first current source 304.
  • the second switch 332 can close (conduct), coupling the second reference sensor 320 to the first current source 304.
  • Method 400 includes generating, from the fourth current, a second voltage at a second terminal of the second reference sensor (step 404). For example, due to the fourth current and the impedance of the second reference sensor 320, a voltage drop across the reference sensor 320 and a voltage at the second terminal 320b are generated.
  • Method 400 includes providing a fifth current to a first terminal of a second active sensor (step 406).
  • a second current source 306 can provide a fifth current to the first terminal 322a of the second active sensor 322.
  • the second current and the fifth current can have the same value.
  • Method 400 can further include electrically uncoupling, from the active sensor, a second current source providing the second current; and coupling, to the second active sensor, the second current source providing the fifth current.
  • the third switch 334 can open (not conduct), electrically uncoupling the active sensor 312 to the second current source 306.
  • the fourth switch 336 can close (conduct), coupling the second active sensor 322 to the second current source 306.
  • the fourth current and the fifth current are constant.
  • the first current source and the second current source are configured to output an equal magnitude of current in a same direction relative to the respective first terminals. For example, currents provided by the first current source 304 and second current source 306 can flow toward a reference potential 320.
  • the reference potential 320 is a reference voltage driven by a voltage source. In another embodiment, the reference potential 320 is a ground.
  • the first current source and the second current source are selected from the group of an athermal voltage source and resistor, a high-impedance athermal transistor current source, and a Wilson current mirror.
  • Method 400 includes driving, at the second voltage, a second terminal of the second active sensor (step 408).
  • the second terminal 320b of the second reference sensor 320 is electrically coupled to the second terminal 322b of the active sensor 322, and the second voltage at this node is driven by voltage driver 308 at output 309.
  • the second voltage is a bias voltage for the second active sensor.
  • the bias voltage is reflective of common mode effects. By biasing the second active sensor at the voltage, these common mode effects can be compensated.
  • the second voltage is driven by an op amp
  • the first terminals of the reference sensors are electrically coupled to a negative input of the op amp.
  • the method further includes feeding back from the second terminal of the reference sensor to the first terminal of the reference sensor using a feedback element.
  • the fourth current causes a voltage drop across the second reference sensor; the second voltage is generated with an amplifier outputting to the second terminal of the second reference sensor; and the first terminal of the second reference sensor is electrically coupled to a negative terminal of the amplifier.
  • Method 400 includes exposing the second active sensor to the sensor image (step 410).
  • the second active sensor 322 is exposed to a sensor image.
  • exposing the second active sensor to the sensor image further includes changing an impedance of the second active sensor.
  • the second active sensor is a second active bolometer pixel.
  • the second active bolometer pixel is exposed to a thermal scene.
  • the impedance of the second active bolometer pixel can change in response to exposure to the thermal scene.
  • exposing the second active sensor to the sensor image includes exposing the second active sensor to LWIR radiation.
  • Method 400 includes measuring a sixth current from the first terminal of the second active sensor to the input of a readout element (step 412). For example, a current entering or exiting input 303 of the readout element 302 is measured.
  • the sixth current is caused by the mechanisms described in this disclosure.
  • the readout data of the currently selected active sensor can be subsequently processed. This process can be repeated for subsequent rows until the entire sensor array has been scanned or until the intended sensors have been scanned.
  • row-to-row readout operation for an active sensor column is described, it is understood that the operation is not limited to one column. The operation can be performed in sequence or simultaneously for more than one column of active sensors using more than one column of reference sensors.
  • FIG. 5 illustrates a sensor readout circuit, in accordance with an embodiment.
  • the readout circuit 500 includes components that are substantially similar to those described in FIGS. 1 and 3. Like components in FIG. 5 are given like numerals as the corresponding components in FIGS. 1 and 3. For the sake of brevity, those like components are not described again with respect to FIG. 5.
  • components of circuit 500 are utilized in conjunction with the readout circuits described elsewhere in the disclosure. Some embodiments include a method of manufacturing the readout circuit 500.
  • the circuit 500 further includes a stage 530 of a readout element that can be substantially similar to the readout elements described in this disclosure.
  • the stage of the readout element is a CTIA.
  • the voltage at the input 503 can ideally equal the voltage of the positive terminal 534 when the reference sensor 510 and the active sensor 512 have the same impedance (for example, when the sensors are both exposed to only the ambient conditions).
  • the voltage at the positive terminal 534 is a reference voltage.
  • the voltage at the positive terminal 534 is a ground voltage.
  • First current buffer 550 is coupled between the reference sensors and the first current source 504.
  • a second current buffer 552 is coupled between the active sensors and the input 503.
  • the current buffers shield the effects of feedback at the input nodes (e.g., input 503, negative terminal of voltage driver 508) from signals generated by the reference and active sensors. For example, undesired current can be injected into the input nodes and modulate the voltages at these nodes. The current buffers prevent the signal currents from being affected by the undesired injected currents.
  • the readout circuit can include no current buffer (e.g., the current sources are electrically coupled to the reference and active sensors) or more than one current buffer (e.g., parallel current buffers, a current buffer for each branch) without departing from the scope of this disclosure.
  • the symbol illustrating current buffers 550 and 552 are used for illustrative purposes only. The symbol does not necessary imply that current buffering is performed using only drivers or amplifiers. It is apparent to a person of ordinary skill in the art that different methods and circuits can be utilized to buffer the current between the sensors and the current sources.
  • the voltage at the output of the CTIA is proportional to an impedance difference between the reference sensor and the active sensor during readout of a sensor.
  • the voltage at the output 536 of the CTIA is V
  • the voltage at the input 503 of the CTIA is V n
  • an effective capacitance at the input of the CTIA is C p
  • the open loop gain of the CTIA is A
  • the feedback capacitor of the CTIA can have a value of CCTIA
  • the impedance of the reference sensor 510 is Z ref
  • the impedance of the active sensor 512 is Z ac tive
  • the bias voltage i.e.
  • V bias the voltage at the second terminal 5l2b) of the active sensor 512 is V bias
  • the first current source 504 can provide a current of Ic
  • the second current source 506 can provide a current of I 2
  • a voltage at reference potential 520 is V ref .
  • the term is a gain coefficient: [0277]
  • the CTIA can be effectively an ideal integrator.
  • the open loop can be substantially large compared to the other variables in the gain coefficient.
  • the variable A can effectively approach infinity.
  • the open loop gain A is greater than 20.
  • the gain coefficient can be approximated:
  • the effective integration capacitance of the CTIA is:
  • the effective integration resistance of the CTIA is:
  • the CTIA has an integration time:
  • the reference sensor 510 and the active sensor 512 are identical in structure. In other words, the two sensors can have the same impedance when exposed to same conditions. Therefore, V can be further simplified:
  • DZ is an impedance difference between the reference and active sensors. Since the terms Ii and x are effectively constant during the readout time, V is proportional to DZ, independent of any other parameters.
  • a sensor image can be computed based only on an impedance difference between the reference and active sensors, independent of any other parameters. It is noted that in addition to removing common mode effects from the measurement, the disclosed constant current readout circuits and methods also yield the elegant result shown above.
  • an exemplary advantage of the disclosed circuits and methods is that an output voltage of the readout circuit can be substantially proportional to an impedance difference of a reference sensor and an active sensor.
  • the sensor image can be simply computed based on the proportional relationship.
  • the simple proportional relationship allows the sensor image to be more easily computed. As a result, less processing is required.
  • the simple proportional relationship includes less varying and unknown elements (in the equations and on the circuit). As a result, the sensor image is more accurate.
  • proportional is not limited to an exact linear relationship. Without departing from the scope of this disclosure, the term“proportional” can be used to describe an approximate linear relationship between two quantities. The term“proportional” can also be used to describe a relationship between two quantities that are different by a scaling factor.
  • the circuit 500 can have an additional load.
  • the additional load can be represented by capacitor 540 at input 532 of the stage 530.
  • the representative capacitor 540 is illustrative and not an actual capacitor or capacitive component electrically coupled to ground.
  • the representative capacitor 540 is an effective capacitance at the input 503 node, which is representative of non-ideal capacitances (e.g., sensor load capacitances, current source capacitances, mismatches, wiring capacitances, parasitics) of the circuit.
  • the readout circuit can include a CDS circuit.
  • the CDS circuit is included as part of the CTIA.
  • the effect on the circuit caused by the additional load is determined. For example, the effective charge caused by the effective representative additional load (e.g., capacitance 540) is sampled. The effect of the additional load is canceled prior to reading out the selected sensor.
  • the additional non-idealities can include voltage and current non-idealities caused by elements of the readout circuit (not symbolically
  • the CDS circuit removes the additional non-idealities as well as the effects of the non-ideal capacitances in the circuit.
  • a method of sensor readout can include converting a current inputted to the readout element to a readout voltage of the readout element.
  • a CTIA can convert the current to a readout voltage of the readout element.
  • a voltage at an output of the CTIA is proportional to an impedance difference between the reference sensor and the active sensor.
  • the readout circuit can further include a CDS circuit.
  • the CDS circuit can remove an offset in the readout circuit.
  • the CDS circuit is included as part of the CTIA.
  • the method further includes: determining an offset generated by the input of the readout element; and canceling the offset prior to measuring the current to the input of the readout element.
  • the circuit can include additional non-idealities such as voltage and current non-idealities caused by elements of the readout circuit (not symbolically represented).
  • the CDS circuit removes the additional non-idealities as well as the offset in the circuit.
  • FIG. 6 illustrates a sensor readout circuit, in accordance with an embodiment.
  • the readout circuit 600 can include components that are substantially similar to those described in FIGS. 1, 3, and 5. For the sake of brevity, those like components are not described again with respect to FIG. 6. In some embodiments, components of circuit 600 are utilized in conjunction with the readout circuits described elsewhere in the disclosure.
  • embodiments include a method of manufacturing the readout circuit 600.
  • the readout circuit 600 includes a third reference sensor 630 and a third current source 608.
  • the third reference sensor 630 includes a first terminal 630a and a second terminal 630b that are electrically coupled to a voltage driver (not shown).
  • the third current source 608 is electrically coupled to the first terminal 630a of the third reference sensor 630, and is configured to output a seventh current reflective of self-heating generated by the third reference sensor 630.
  • the value of the second current provided by second current source 606 adjusts in accordance with the seventh current.
  • the second current source is substantially similar to the second current described in this disclosure
  • the third reference sensor is a reference or blind bolometer pixel.
  • the seventh current is provided by a controlled current source.
  • the controlled current source is controlled using feedback loop 616, which tracks the voltage at the first terminal 630a of the third reference sensor 630, and hence, its self-heating.
  • the seventh current can change due to the tracked self heating of the third reference sensor 630, which is reflective of self-heating experienced by the active sensors.
  • the voltage at the first terminal 630a is held constant by the op-amp of feedback loop 616 in a negative feedback configuration.
  • the output voltage of the op-amp updates to track the changes in current due to self-heating.
  • the seventh current is mirrored to the second current source 606, which is electrically coupled to active sensor 612 to compensate for self-heating of the selected active sensor.
  • a negative feedback amplifier is shown merely for exemplary purposes. It is understood that other components and methods can track and control the currents 606 and 608 without departing from the scope of the invention.
  • a voltage driver is not shown to drive the bias voltage, it is understood that a voltage driver can be electrically coupled across the reference sensor to drive the bias voltage, as described in this disclosure.
  • one reference column and one active column are illustrated, it is understood that one or more reference columns can track self-heating and one or more active columns can be compensated for self-heating.
  • FIG. 7 illustrates a method 700 of current adjustment, in accordance with an embodiment.
  • a current provided to an active bolometer pixel is compensated for self-heating by tracking a blind bolometer pixel.
  • Method 700 includes: providing a seventh current to a first terminal of a third reference sensor (step 702), the seventh current reflective of self-heating generated by the third reference sensor; and adjusting a value of the second current in accordance with the seventh current (step 704).
  • Method 700 can be achieved using readout circuit 600 or other suitable self-heating compensating components.
  • the seventh current is provided by third current source 608 and tracked by feedback loop 616.
  • the tracked current is mirrored to a current (e.g., current provided by second current source 606) provided to an active sensor.
  • the voltage across the reference sensor is kept constant.
  • the third reference sensor 630 is not exposed to ambient conditions and no voltage driver is electrically coupled in parallel with the third reference sensor 630.
  • the third reference sensor does not generate the bias voltage and adjust the average bias current to track ambient changes.
  • FIG. 8 illustrates a sensor bias circuit, in accordance with an embodiment.
  • the readout circuit 800 can include components that are substantially similar to those described in FIGS. 1, 3, 5, and 6. For the sake of brevity, those like components are not described again with respect to FIG. 8.
  • components of circuit 800 are utilized in conjunction with the readout circuits described elsewhere in the disclosure. Some embodiments include a method of manufacturing the circuit 800.
  • the sensor bias circuit 800 separately tracks the ambient condition and is independent of the described self-heating compensation components.
  • Circuit 800 includes a reference sensor 840, a current source 810, and a voltage driver 808.
  • the reference sensor 802 is a thermally shorted (blind or reference) bolometer pixel.
  • the current source 810 and the voltage driver 808 is substantially the same as the first current source and voltage driver described in the disclosure.
  • the bias voltage which tracks the ambient conditions, is generated in a substantially the same manner as described in this disclosure.
  • the bias voltage output 809 is electrically coupled to the bias voltage nodes of the readout circuits described in this disclosure to generate the active sensor bias currents.
  • a voltage follower is electrically coupled between the bias voltage node and second terminals of one or more active sensors, in a manner similar to the voltage followers described herein.
  • the voltage follower acts as a voltage buffer.
  • the voltage follower can reduce the output loading of the voltage driver 808.
  • an active column includes more than one active sensor.
  • the bias voltage is driven to more than one active column.
  • the loading (e.g., capacitive load) at the active bias voltage node increases as the size of the column and/or the number of columns being driven increases.
  • the voltage follower can maintain the size of the voltage driver 808 and a desirable active bias voltage response.
  • FIG. 9 illustrates a sensor readout system, in accordance with an embodiment.
  • Sensor readout system 900 includes sensor readout circuit 902 and ADC 904.
  • the sensor readout circuit 902 can be a readout circuit described in this disclosure.
  • the sensor readout circuit 902 can electrically couple to ADC 904.
  • Some embodiments include a method of manufacturing the circuit 900.
  • the ADC can sample a current or charge from the first terminal of the active sensor to the input of the readout element, as described in this disclosure.
  • the ADC 904 includes one or more Sigma-Delta ADCs.
  • a first stage of the ADC is a CTIA.
  • common components e.g., CTIA
  • CTIA common components
  • a method of sensor readout includes sampling a voltage generated by the current or charge to the input of the readout element.
  • the readout element can include a Sigma-Delta ADC, and the voltage being sampled is generated by a CTIA.
  • a first current buffer is coupled between reference sensors and a first current source.
  • a second current buffer is coupled between active sensors and an input of the Sigma-Delta ADC.
  • the current buffers shield the effects of feedback at input nodes (e.g., the input of the Sigma-Delta ADC) from signals generated by reference and active sensors. For example, undesired current can be injected into the input nodes and modulate the voltages at these nodes.
  • the current buffers reduce the undesired injected currents’ effect on the signal currents.
  • the input current of the CTIA is a difference generated by an active bolometer pixel exposed to a thermal scene.
  • the CTIA is a first stage of the Sigma- Delta ADC.
  • the senor calibration circuits include a calibration sensor and a calibration readout element.
  • the sensor calibration circuits include a calibration current source.
  • a shutter is included with the sensor calibration circuits.
  • the methods include measuring a voltage of the calibration sensor and computing a calibrated readout voltage based on the measured calibration sensor voltage. In some embodiments, the methods include measuring a readout voltage of a readout element electrically coupled to the calibration current source and computing an output based on the readout voltage. In some embodiments, the methods include measuring readout voltages when the shutter is closed and when the shutter is opened and computing a difference between the readout voltages.
  • the disclosed circuits and methods remove noise at reduced costs.
  • the circuits presented herein efficiently and compactly remove noises in the sensor array.
  • the clarity of measured sensor images can be improved.
  • FIG. 10 illustrates a sensor readout circuit 1000, in accordance with an
  • the sensor readout circuit 1000 includes readout elements l002a and l002b, current sources l004a to l004c, a voltage driver 1006, reference sensors l008a and l008b, active sensors lOlOa to lOlOd, and switches l0l6a to l0l6h. Some embodiments include a method of manufacturing the readout circuit 1000.
  • elements of the sensor readout circuit 1000 correspond to elements of the sensor readout circuit 100.
  • readout element l002a corresponds to readout element 102
  • current source l004a corresponds to second current source 106
  • current source l004c corresponds to first current source 104
  • voltage driver 1006 corresponds to voltage driver 108
  • reference sensor l008a corresponds to reference sensor 110
  • active sensor lOlOa corresponds to active sensor 112.
  • the topology uses one voltage driver, which provides a bias voltage. Without adding circuitry to reduce undesired common mode effects, the topology can reduce undesired common effects without increasing complexity, size, and cost, introducing more parasitics and unknowns, consuming more power, and adding noise inducing components.
  • the reference sensors l008a and l008b are shielded from the sensor image and the active sensors lOlOa to lOlOd are exposed to the sensor image.
  • the reference sensors can be exposed to an ambient condition common to the reference sensors and active sensors.
  • the reference sensor is a reference or blind bolometer pixel that is exposed to ambient temperatures, but is not exposed to a thermal scene
  • the active sensor is an active bolometer pixel, which is exposed to both the ambient temperatures and the thermal scene.
  • the sensors include two terminals and can have a variable impedance value between the two terminals that depends on a sensor image.
  • each row is readout sequentially.
  • row control l0l4a is driven by a voltage that turns on the switches of the corresponding row (e.g., switches l0l6a to l0l6d) while row control l0l4b is driven by a voltage that turns off the switches of the corresponding row (e.g., switches l0l6e to l0l6h).
  • row control l0l4b is driven by a voltage that turns on the switches of the corresponding row (e.g., switches l0l6e to l0l6h) while row control l0l4a is driven by a voltage that turns off the switches of the
  • corresponding row e.g., switches l0l6a to l0l6d.
  • switches of a corresponding row When switches of a corresponding row are turned on, the active and reference sensors of the corresponding row are electrically coupled to the bias voltage node 1012 and corresponding current sources while sensors of the other rows are electrically uncoupled from the bias voltage node 1012 and corresponding current sources. It is understood that the described readout operation is exemplary.
  • a selected reference sensor generates an adjustable bias voltage at the bias voltage node 1012 that tracks both ambient conditions and self-heating.
  • the readout circuit operates in a constant current mode. Since no other branch is electrically coupled between current source l004c and the selected reference sensor, the current through the selected reference sensor is constant.
  • the impedance of the reference sensor stabilizes to a value that is reflective of the ambient conditions.
  • the impedance of the sensor can be substantially fixed at a stable state, it is understood that the impedance of the reference sensor can vary according to the ambient conditions.
  • a voltage drop is generated across the reference sensor due to the current and the reference sensor impedance.
  • the voltage at the bias voltage node 1012 is dictated by the voltage drop.
  • the voltage at the bias voltage node 1012 is driven by voltage driver 1006.
  • voltage driver 1006 can act substantially as an ideal voltage source. In other words, the voltage driver 1006 can provide (or absorb) the necessary current to maintain the generated voltage at the bias voltage node 1012.
  • voltage driver 1006 The symbol illustrating voltage driver 1006 is used for illustrative purposes only. It is apparent to a person of ordinary skill in the art that different methods and circuits can be utilized to drive the bias voltage.
  • the bias voltage can be significant because it is reflective of common mode effects, such as self-heating and ambient conditions, observed by the reference sensor.
  • the selected active sensors are biased at the bias voltage, and the common mode effects (which can disadvantageously reduce the dynamic range of subsequent stages) have been effectively compensated, because the bias voltage is reflective of common mode conditions.
  • an active sensor is substantially the same as a reference sensor, and the current sources l004a-l004c provide substantially the same current.
  • the readout elements can have a low input resistance, such as an input of a charge amplifier.
  • a low input resistance such as an input of a charge amplifier.
  • the sensors are located on a glass substrate.
  • the glass substrate includes a plurality of TFTs that are used as switches for the sensor array (e.g., switches l0l6a-l0l6h).
  • non-sensor and non switching elements off the array e.g., readout elements, voltage drivers, current sources
  • FIG. 10 illustrates the sensor readout circuit as having a two-by-two active sensor array, two reference sensors, and other described elements, it is understood that the disclosed sensor readout circuit is exemplary.
  • the measured current or charge is independent of common mode effects, it may be susceptible to noise, which affects accuracy of the sensor image measurement and clarity of the sensor image.
  • bolometer noise can be overwhelming and the thermal image can be distorted due to noise.
  • Noise in a bolometer array can include non- pattemed noises and patterned noises. Examples of non-pattemed noises include l/f noise, thermal noise and process dependent noises in the pixels. Examples of patterned noises include row-to-row patterns and column-to-column patterns.
  • FIG. 11 illustrates a sensor calibration circuit, in accordance with an embodiment.
  • the sensor calibration circuit 1100 includes a calibration sensor 1102, a calibration readout element 1104, and a current source 1106.
  • the calibration readout element 1104 is substantially the same as one of readout elements l002a or l002b.
  • current source 1106 is substantially the same as one of the current sources l004a, l004b, or l004c.
  • the calibration sensor 1102 can include two terminals: a first terminal electrically coupled to bias voltage node 1108 of sensor readout circuit 1110 and a second terminal electrically coupled to the calibration readout element 1104 and current source 1106.
  • the sensor readout circuit 1110 is substantially the same as sensor readout circuit 1000.
  • the bias voltage node 1108 can be shared by active sensors of the sensor readout circuit 1110.
  • the calibration sensor is shielded from a sensor image that is exposed to active sensor elements of the sensor readout circuit 1110.
  • the sensor readout circuit 1110 is a bolometer readout circuit that measures a thermal image; the bolometer readout circuit includes a full array of bolometers and associated row and column readout circuitries.
  • the calibration sensor electrically coupled to the bolometer readout circuit is a calibration bolometer.
  • the sensor readout circuit 1000 is merely exemplary. It is understood that the sensor readout circuit 1110 can have different configurations and components without departing from the scope of the disclosure.
  • the impedance of calibration sensor 1102 is substantially the same as the nominal impedance of an active sensor in the calibration readout circuit 1110.
  • the impedance ratio of the two sensors is one.
  • the impedance ratio is temperature independent.
  • the nominal impedance of a sensor is the impedance of the sensor when the sensor is not exposed to a sensor image.
  • the nominal impedance of the active sensor is in the range of 10 kiloohms to 100 megaohms.
  • the calibration sensor 1102 has a higher electrical carrier count than an electrical carrier count of an active sensor (e.g., one of active sensors lOlOa to lOlOd) in the calibration readout circuit 1110.
  • an active sensor e.g., one of active sensors lOlOa to lOlOd
  • the calibration sensor has a higher electrical carrier count than the electrical carrier count of the active sensor if the calibration sensor has a greater quantity of electrically conductive material compared to the active sensor.
  • the calibration sensor and the active sensor can have the same impedance while the calibration sensor has a higher electrical carrier count when the calibration sensor and the active sensor have the same aspect ratio (e.g., both are squares), but the physical dimensions of the calibration sensor are greater than those of the active sensor.
  • the calibration sensor is formed by more than one sensor; the sensors are connected in series and parallel to achieve total impedance that is substantially the same as the active sensor. Since the calibration sensor has a higher electrical carrier count, the calibration sensor has less l/f noise compared to an active sensor.
  • the calibration sensor and the active sensor are fabricated from materials having a same temperature coefficient of resistance (TCR).
  • the calibration sensor and active sensors are created from one or more of amorphous silicon, vanadium oxide, platinum, titanium, titanium oxide, tungsten oxide, and molybdenum.
  • the calibration sensor and the active sensor are fabricated from a substantially same material.
  • the calibration readout element is an analog-to-digital converter (ADC).
  • ADC analog-to-digital converter
  • the calibration readout element is an ADC that is
  • the calibration readout circuit 1100 is used to calibrate for noise in the measurement of active sensors. Specifically, the calibration readout circuit 1100 is used to calibrate the measurement for row-to-row pattern noises, which are noises that varies from one row to another.
  • the readout voltages of selected active sensors are measured with respective readout elements.
  • the readout voltages of selected active sensors are generated by currents caused by the active sensor’s exposure to a sensor image.
  • the readout voltage of the calibration sensor is created by a current traversing between the first and second terminals of the calibration sensor and is measured by the calibration readout element 1104. The current is generated from current source 1106.
  • a calibrated readout voltage can be computed for a j* column while the i* row is being measured:
  • the index (i, j) is associated with a specific active sensor of the selected sensors. For example, the sensors of the i* row are being selected for readout and each of the selected sensors corresponds to a j* column. Although the index (i,j) is used to described an exemplary sensor, it is understood that the subscripts can be used to describe any active sensor. [0344]
  • the quantity A ca i,ij is the calibrated readout voltage associated with sensor (i,j)’s exposure to a sensor image.
  • the quantity A s j is the (non-calibrated) readout voltage of sensor (i, j) at a respective readout element of the j* column.
  • the quantity A IM is the readout voltage of the calibration sensor when the bias voltage node is driven with a bias voltage associated with the reference sensor of i* row (e.g., bias voltage associated with the common mode conditions of the i* row).
  • Z M is the impedance of the calibration sensor
  • Z S y is the nominal impedance of the sensor (i,j) (e.g., when shielded from the sensor image).
  • the two impedances are substantially equal, so the factor (Z M /Z ⁇ ) is one.
  • equation (14) removes undesired row-to-row pattern noises, such as noise in the bias voltage, from the active sensor readout voltage.
  • the inclusion of the calibration sensor, an associated readout element, and an associated current source may be important for deriving a measurement that is free of row-to-row pattern noises.
  • the bias voltage may not be measured directly and the effects of bias voltage noise may not be correctly captured, because, due to pixel self-heating, the bias voltage is a time varying voltage during ADC conversion time. Since undesired bias voltage effect can be removed for each row, the need to calibrate the skimming current sources can be eliminated, reducing the complexity of the readout circuit.
  • the exemplary sensor calibration shows how a selected row of sensors during readout can be calibrated with the calibration sensor, removing undesired row-to-row pattern noises, such as bias voltage noise.
  • the described method is repeated for other selected rows during readout. For example, after a selected first row of sensors is calibrated with the calibration sensor electrically coupled to a reference sensor of the first row (e.g., reference sensor l008a) (i.e., bias voltage associated with the common mode conditions of the first row), the first row of sensors is deselected and a second row of sensors is selected for readout.
  • a reference sensor of the first row e.g., reference sensor l008a
  • the selected second row of sensors is calibrated with the calibration sensor, which is now electrically coupled to a reference sensor of the second row (e.g., reference sensor l008b) (i.e., bias voltage associated with the common mode conditions of the second row).
  • a reference sensor of the second row e.g., reference sensor l008b
  • bias voltage associated with the common mode conditions of the second row i.e., bias voltage associated with the common mode conditions of the second row.
  • Row-to-row pattern noises such as bias voltage noise associated with the second row, can be removed in a similar manner as described.
  • FIG. 12 illustrates a method 1200 of sensor calibration, in accordance with an embodiment.
  • Method 1200 includes electrically coupling a first terminal of a calibration sensor to a bias voltage node shared by a plurality of active sensors (step 1202).
  • the calibration sensor 1102 is electrically coupled to bias voltage node 1108.
  • Method 1200 includes electrically coupling a second terminal of the calibration sensor to a calibration readout element (step 1204).
  • the calibration sensor 1102 is electrically coupled to the calibration readout element 1104.
  • Method 1200 includes exposing the plurality of active sensors to a sensor image (step 1206). For example, referring to FIG. 11, a plurality of active sensors in sensor readout circuit 1110 is exposed to a sensor image.
  • Method 1200 includes shielding the calibration sensor from the sensor image (step 1208).
  • the calibration sensor 1102 is shielded from the sensor image.
  • Method 1200 includes measuring, with a readout element, a readout voltage of an active sensor of the plurality of active sensors (step 1210). For example, referring to FIG. 11, A Sij , the non-calibrated readout voltage of sensor (i, j), is measured.
  • Method 1200 includes measuring, with the calibration readout element, a readout voltage of the calibration sensor (step 1212). For example, referring to FIG. 11, the readout voltage of calibration readout element 1104 is measured.
  • Method 1200 includes computing a calibrated voltage (step 1214).
  • the calibrated voltage is computed as a difference between (1) the readout voltage of the active sensor and (2) the readout voltage of the calibration sensor weighted by a ratio between an impedance of the calibration sensor and an impedance of the active sensor.
  • the quantity A cai,ij is computed based on the measured quantities and sensor impedances.
  • the impedance of the calibration sensor is the same as the impedance of the active sensor, and an electrical carrier count of the calibration sensor is greater than an electrical carrier count of the active sensor.
  • the ratio is one. In some embodiments, the ratio is temperature independent.
  • the calibration sensor and the active sensor are made from materials having a same TCR.
  • the method 1200 includes electrically coupling a current source of a plurality of current sources to the second terminal of the calibration sensor and to the calibration readout element; electrically coupling a column of a plurality of columns of active sensors to the readout element, the column of active sensors including the active sensor; and electrically coupling a second current source of the plurality of current sources to the readout element.
  • current source 1106 is electrically coupled to calibration readout element 1104, a column of active sensors is electrically coupled to a readout element in the sensor readout circuit 1000, and a current source is electrically coupled to a readout element in the sensor readout circuit 1000.
  • the method 1200 includes closing a shutter; measuring, with the readout element, a first readout voltage corresponding to the closed shutter; and measuring, with the calibration readout element, a second readout voltage corresponding to the closed shutter; and after computing the calibrated voltage, computing a second difference between (1) the calibrated voltage and a difference between (2a) the first readout voltage and (2b) the second readout voltage weighted by the ratio, where the second difference is a shutter calibrated voltage. Examples of these embodiments will be described below with reference to equations (22) and (23).
  • the calibration readout element includes an ADC. In some embodiments, the readout element includes an ADC.
  • the plurality of active sensors and the calibration sensor are bolometers, and the sensor image is a thermal image.
  • FIG. 13 illustrates a sensor calibration circuit, in accordance with an embodiment.
  • the sensor calibration circuit 1300 includes calibration current sources l302a and l302b and switches l304a to 1304F Some embodiments include a method of manufacturing the circuit 1100.
  • the sensor calibration circuit 1300 is electrically coupled to sensor readout circuit 1310, which includes sections l3l0a and l3l0b. In some examples, the sensor readout circuit 1310 is sensor readout circuit 1000.
  • the switches l304c and l304d are associated with a first column l3l2a of active sensors.
  • the switches l304e and l304f are associated with a second column 13 l2b of active sensors, different from the first column.
  • the switches l304c and l304e can electrically couple or electrically uncouple the calibration current source and a readout element of the column.
  • the switches l304d and l304f can electrically couple or electrically uncouple active sensors of their respective column and a readout element of the column (e.g., readout elements l002a and l002b).
  • the readout element is an ADC.
  • the sensor readout circuit 1000 is merely exemplary and any number of columns and any number of switches can electrically couple or uncouple the calibration current source or active sensors and the active sensor columns.
  • the columns of sensors are symbolically included in a box that represents sensor readout circuit 1310 and the calibration circuit 1310 is symbolically illustrated outside the representative box, it is understood that the term“column” is not necessarily arranged in a straight line.
  • a column of sensors is associated with one readout element.
  • a column of sensors can come in any shape or form without departing from the scope of the disclosure.
  • the switches l304a and l304b can electrically couple the current sources l302a and l304b, respectively, and a column that is under calibration. In an embodiment, the switches l302a and l304b electrically couple one of the current sources and the sensor columns at a time.
  • FIG. 13 illustrates the sensor calibration circuit 1300 as having two current sources and two associated switches, it is understood that any number of calibration current sources and associated switches can exist without departing from the scope of the disclosure.
  • the sensor calibration circuit 1300 has one calibration current source and one associated switch.
  • a first column is in calibration mode; a readout element of the first column is electrically coupled to a first calibration current source of the calibration current sources.
  • the column l3l2a is in calibration while a first row of sensors is being readout.
  • Switch l304c is closed (conducting) and switch l304d is opened (non- conducting).
  • a first calibration current of the calibration current sources e.g., calibration current source l302a through switch l304a or calibration current source l302b through switch l304b
  • the readout element of the first column e.g., readout element l002a.
  • the column 13 l2b is in readout mode while the first row of sensors is being readout.
  • Switch l304e is opened (non-conducting) and switch l304f is closed (conducting).
  • the currently selected active sensor e.g., active sensor lOlOb
  • the currently selected active sensor is electrically coupled to the column’s readout element (e.g., readout element l002b).
  • the readout voltages of the columns are measured.
  • the readout voltage caused by the first calibration current e.g., readout voltage of the column electrically coupled to calibration current source l302a or calibration current source l302b, readout voltage of readout element l002a
  • Ai j (t) can be denoted as Ai j (t).
  • the first column may still be in calibration, and the other columns may still be in the readout mode.
  • the readout element of the first column is electrically uncoupled from the first calibration current source and electrically coupled to a second current source of the calibration current sources.
  • the column l3l2a is in calibration mode while a first row of sensors is being readout.
  • Switch l304c is closed (conducting), and switch l304d is opened (non-conducting).
  • a second calibration current source of the calibration current sources e.g., calibration current source l302b through switch l304b or calibration current source l302a through switch l304a
  • the readout voltage caused by the second calibration current (e.g., from calibration current source l302a or calibration current source l302b), can be denoted as A 2j (t).
  • the values Ai j (t) and A3 ⁇ 4(t) capture a drift of the respective readout element (e.g., readout element l002a).
  • readout voltage of any active sensor in the calibrated column can be calibrated.
  • the readout voltage of the active sensor can be denoted as A Sjj (t), where an active sensor associated with the i th row and j th column is being measured.
  • the selected active sensor of the calibrated column e.g., active sensor lOlOa
  • the current readout voltage of this sensor is not measured (e.g., readout voltage associated with active sensor lOlOa).
  • a previous value of A Sjj or an interpolated value based on adjacent sensors is used for Asij(t) .
  • a current readout voltage A Sjj (t) is measured even when a column is being calibrated; the calibration current sources are electrically uncoupled from the readout element and the active sensor is electrically coupled to the readout element, where the current readout voltage of the active sensor is measured.
  • an output D Sjj (t) can be computed for a column j* while the i th row is being measured:
  • the quantity D Sjj (t) is a term that is linear to the current into the readout element of a column j (e.g., the current caused by the sensor image, as described). Since equation (15) accounts for the drift in the readout element, the term is independent of effects such as ADC gain, offset, skimming currents, and any time- varying quantities except I(t), which is the current into a respective readout element.
  • the quantity D Sy (t) is a stabilized digital output, which is a stabilized version of an output of a readout element (e.g., an ADC).
  • DI I 2 -Ii Ii is the first calibration current.
  • I 2 is the second calibration current.
  • the quantities Aq(t) and A3 ⁇ 4(t) are used to compute subsequent outputs corresponding to subsequent rows of the column that are being read out, until the column is calibrated again (i.e., Ai j (t) and A3 ⁇ 4(t) are updated).
  • a second row (e.g., active sensors lOlOc-lOlOd) is being selected for readout and the first column is no longer being calibrated (since the quantities Aq(t) and A3 ⁇ 4(t) corresponding to the first column have been measured).
  • the column l3 l2a is in readout mode while the second row of sensors is being readout.
  • Switch l304c is opened (non-conducting), and switch l304d is closed (conducting).
  • the currently selected active sensor (e.g., active sensor lOlOc) is electrically coupled to the column’s readout element (e.g., readout element l002a).
  • the term A Sij (t) is the readout voltage of the active sensor lOlOc.
  • an output D Sy (t) can be computed for the active sensor of the first column and second row.
  • the output D Sij (t) can be computed for any active sensor of the column using equation (15) when a respective sensor is being readout.
  • an output D Sjj (t) is computed.
  • the quantity D Sjj (t) can be linearly proportional to the active sensor current (i.e., current caused by the sensor image), free of any other time-varying or column-dependent noise parameter. Equation (15) removes undesired column-to-column pattern noises, such as mismatches between skimming currents, ADC gains, and ADC offsets. In addition, these undesired noises can be removed while the active sensors are being readout.
  • the configuration described with respect to FIG. 4 can allow calibration and readout to be performed in parallel. Therefore, under this configuration, dedicated calibration time (i.e., no readout while calibration is being performed) may not be needed and more rows can be readout during a given amount of time, improving performance and accuracy of the readout circuit.
  • calibration currents e.g., calibration current sources l302a and l302b
  • associated switches e.g., switches l304a, l304b, l304c, and l304e
  • a quantity e.g., the output
  • column-dependent noises such as skimming current mismatches, ADC gain mismatches, and ADC offset mismatches, may be reflected on the sensor image, distorting the clarity of the sensor image or dedicated calibration time would be needed to remove these noises, degrading the performance of the readout circuit.
  • one calibration current source (e.g., calibration current source l302a or l302b) is used for calibration, instead of two calibration current sources.
  • only the steps associated with the first calibration current source are performed (i.e., with one calibration current source, the steps associated with the second time of a row readout time are not performed).
  • a readout element of the column is electrically coupled to only one of the calibration current sources.
  • the column l3l2a is in calibration mode while a first row of sensors is being readout.
  • Switch l304c is closed (conducting), and switch l304d is opened (non conducting).
  • a first calibration current of the calibration current sources e.g., calibration current source l302a through switch l304a or calibration current source l302b through switch l304b
  • the readout element of the first column e.g., readout element l002a.
  • the column 13 l2b is in readout mode while the first row of sensors is being readout.
  • Switch l304e is opened (non-conducting), and switch l304f is closed (conducting).
  • the currently selected active sensor e.g., active sensor lOlOb or lOOOd
  • the currently selected active sensor is electrically coupled to the column’s readout element (e.g., readout element l002b).
  • the readout voltages of the columns are measured.
  • the readout voltage caused by the calibration current e.g., readout voltage of the column electrically coupled to calibration current source l302a or calibration current source l302b, readout voltage of readout element l002a
  • a j (t) can be measured in the same manner as described (i.e., interpolated with adjacent sensors or estimated with a previous measurement when the respective column is in calibration; active sensor readout voltage is measured when the respective column is in readout mode).
  • an output D slj (t) can be computed for a column j th while the 1 th row is being measured:
  • the above calibration methods with the calibration current(s) can be performed throughout the sensor readout circuit during readout.
  • the exemplary methods can be repeated by putting different columns in calibration.
  • a first row is selected for readout.
  • a first column is in the calibration mode, as described, while the remaining columns are in the readout mode; the quantities Aq(t) and A 2j (t) associated with the first column are measured and outputs D(t) associated with the active sensors of the column can be computed using the method as described.
  • a second row is selected for readout.
  • a second column is in calibration, which is similar to how the first column is calibrated, as described.
  • the remaining columns e.g., columns other than the second column
  • the quantities Aq(t) and A 2j (t) associated with the second column are measured (e.g., readout voltages caused by the first calibration current and the second calibration current on the readout element l002b) and outputs D(t) associated with the active sensors of the second column can be computed using the method as described (i.e., interpolated with adjacent sensors or estimated with a previous measurement when the respective column is in calibration; active sensor readout voltage is measured when the respective column is in readout mode).
  • outputs D(t) associated with the active sensors of the column can be computed using the method as described (i.e., a respective active sensor readout voltage (e.g., A slj (t)) is measured; since Aq(t) and A3 ⁇ 4(t) are known after calibration, the terms can yield corresponding outputs D slj (t)).
  • a respective active sensor readout voltage e.g., A slj (t)
  • Aq(t) and A3 ⁇ 4(t) are known after calibration, the terms can yield corresponding outputs D slj (t)).
  • the frequency of calibration mode activation may depend on system requirements or the noise environment without departing from the scope of the disclosure.
  • one column is being calibrated during each row readout time, it is understood that more than one column may be calibrated without departing from the scope of the disclosure.
  • the quantities Ai j (t) and A 2j (t) may be measured for multiple columns during a row readout time and the multiple columns are calibrated during one row readout time.
  • the calibration mode is enabled periodically.
  • the calibration period is defined by a time between a first calibration of the particular column and subsequent calibration of the particular column (i.e., time between updates of Aq and/or A 2j for the particular column).
  • the calibration period is determined by a drift of the readout element. For example, if the readout element drifts quickly, the calibration period is short. In another example, if the readout element drifts slowly, the calibration period is long.
  • the column is calibrated when different rows are being readout. For example, during a first calibration time, a first column is calibrated when a first row is being readout; during a second calibration time, the first column is calibrated when a second row is being readout.
  • a same active sensor’s actual readout voltage would not be always left out (e.g., would not always being estimated with a previous value or an interpolated value).
  • the current readout voltage of the active sensor of the first column and first row would always be interpolated with adjacent active sensors or estimated with previous readout voltages.
  • calibration mode is enabled every one second.
  • calibration mode frequency is determined by noise characteristics of the sensor readout circuit.
  • the column selected for calibration mode is based on noise characteristics of the sensor readout circuit.
  • FIG. 14 illustrates a method 1400 of sensor calibration, in accordance with an embodiment.
  • Method 1400 includes electrically coupling a readout element to an active sensor (step 1402).
  • a readout element of sensor readout circuit 410 is electrically coupled to an active sensor of sensor readout circuit 1310.
  • Method 1400 includes measuring, with the readout element, a first readout voltage of the active sensor (step 1404). For example, referring to FIG. 13 and equations (15) and (19), a first readout voltage (e.g., A slj (t)) is measured with the readout element.
  • a first readout voltage e.g., A slj (t)
  • Method 1400 includes electrically uncoupling the readout element from the active sensor (step 1406).
  • the readout element of sensor readout circuit 1310 is electrically uncoupled from the active sensor of sensor readout circuit 1310.
  • Method 1400 includes electrically coupling a calibration current to the readout element (step 1408).
  • a calibration current For example, referring to FIG. 13, calibration current l302a or calibration current l302b is electrically coupled to the active sensor of sensor readout circuit 1310.
  • Method 1400 includes measuring, with the readout element, a second readout voltage caused by the calibration current (step 1410). For example, referring to FIG. 13 and equations (15) and (19), a second readout voltage (e.g., A j (t), Aq(t)) is measured with the readout element.
  • a second readout voltage e.g., A j (t), Aq(t)
  • Method 1400 includes computing an output based on (1) the first readout voltage and (2) the second readout voltage (step 1412).
  • the output is proportional to a readout current of the active sensor. For example, referring to equations (15) and (19), the output D(t) is computed based on the first and second readout voltages.
  • the method 1400 includes electrically coupling a respective active sensor of a plurality of active sensors to a respective readout element of a plurality of readout elements; measuring, with the respective readout element, a first readout voltage of the respective active sensor; electrically uncoupling the respective readout element from the respective active sensor; electrically coupling the calibration current to the respective readout element; measuring, with the respective readout element, a second readout voltage caused by the calibration current on the respective readout element; and computing an output proportional to a readout current of the respective active sensor based on (1) the first readout voltage of the respective active sensor and (2) the second readout voltage caused by the calibration current.
  • a column 13 l2b is calibrated (i.e., A j (t) associated with column 13 l2b is measured, the drift of the column is measured) after column l3l2a is calibrated (i.e., A j (t) associated with column l3l2a is measured, the drift of the column is measured).
  • the method 1400 includes, after computing the first output: electrically uncoupling the calibration current source from the readout element; electrically coupling the readout element to a second active sensor, the second active sensor belonging to a same column as the first active sensor; measuring, with the readout element, a third readout voltage of the second active sensor; and computing a second output proportional to a readout current of the second active sensor based on (1) the third readout voltage and (2) the second readout voltage caused by the calibration current.
  • the first output electrically uncoupling the calibration current source from the readout element; electrically coupling the readout element to a second active sensor, the second active sensor belonging to a same column as the first active sensor; measuring, with the readout element, a third readout voltage of the second active sensor; and computing a second output proportional to a readout current of the second active sensor based on (1) the third readout voltage and (2) the second readout voltage caused by the calibration current.
  • an output D(t) associated with a second row on column l3l2a can be computed based on A j (t) and readout voltage of the active sensor on the second row.
  • a time between successive measurements of the second readout voltage on the same column caused by the calibration current is a calibration period.
  • the calibration period is one second.
  • the calibration period is based on a drift of the readout element.
  • different rows are being readout during the successive measurements of the second readout voltage.
  • the quantity A j (t) is measured at a first time for column 13 l2a when a first row is readout.
  • the quantity A j (t) is measured for column l3l2a when a second row, different from the first row, is readout.
  • the method 1400 includes electrically uncoupling the readout element from the first calibration current source; electrically coupling the readout element to a second calibration current source; and measuring, with the readout element, a third readout voltage caused by the second calibration current on the readout element, where the output is further based on the third readout voltage caused by the second calibration current.
  • both calibration currents l302a and l302b are used to measure the quantities Aq(t) and A 2j (t), and the output D(t) is based on the quantities Aq(t) and A 2j (t).
  • the readout element includes an ADC.
  • the method 1400 includes closing a shutter; computing the output corresponding to a closed shutter; and computing a difference proportional to an impedance difference of the active sensor caused by a sensor image between (1) the output corresponding to an opened shutter and (2) the output corresponding to the closed shutter. Examples of these embodiments will be described below with reference to equations (22) and (23).
  • the first active sensor is a bolometer exposed to a thermal scene.
  • FIG. 15 illustrates a sensor calibration circuit, in accordance with an embodiment.
  • the calibration circuit 1500 includes calibration sensor circuit 1520 and calibration current circuit 1530.
  • the calibration circuit 1500 is a combined circuit that performs the calibration methods as described.
  • calibration sensor circuit 1520 can be similar to sensor calibration circuit 1100.
  • Calibration current circuit 1530 can be similar to calibration current circuit 1300.
  • the calibration circuit 1500 is electrically coupled to sensor readout circuit 1510.
  • the sensor readout circuit 1510 can be substantially similar to sensor readout circuit 1000. It is understood that readout circuit 1510 can include a sensor array of any size and corresponding readout circuities without departing from the scope of the disclosure. Some embodiments include a method of manufacturing the circuit 1500.
  • FIG. 16 illustrates a sensor calibration circuit, in accordance with an embodiment.
  • sensor calibration circuit 1600 is an embodiment of the sensor calibration circuit 1500.
  • the sensor calibration circuit 1600 includes calibration sensor circuit 1620 and calibration current circuit 1630.
  • the sensor calibration 1600 is electrically coupled to sensor readout circuit 1610, which includes section l6l0a and l6l0b, as shown. It is understood that FIG. 16 is illustrative and its elements are symbolic. Other configurations of the sensor calibration circuit 1600 and connections between the sensor calibration circuit and the sensor readout circuit 1610 can exist without departing from the scope of the disclosure. Some embodiments include a method of manufacturing the circuit 1600.
  • the combined calibration circuit (e.g., sensor calibration circuit 1600) concurrently performs the calibration methods associated with FIG.s 11 and 13. For example, while a selected row of sensors is being readout, a calibration sensor is used to calibrate the bias voltage associated with the selected row and the calibration currents are used to calibrate the ADCs and skimming currents for particular column(s).
  • the combined calibration using the calibration sensor and calibration currents includes substantially the same steps as each of the individual methods as described. For the sake of brevity, the similar steps are not repeated here.
  • a Mi (t) is the readout voltage of the calibration readout element when the first calibration current is electrically coupled to the calibration readout element and A M 2( is the readout voltage of the calibration readout element when the second calibration current is electrically coupled to the calibration readout element.
  • a blank row readout time e.g., one row readout time delay
  • the bias voltage is calibrated before the calibration sensor is electrically uncoupled from the calibration readout element to make the A Mi (t) and A M 2(t) measurements.
  • equations (15) and (20) can be combined into equation (14).
  • equation (20) is reduced to be substantially similar to equation (19) in a similar manner that equation (20) is derived from equation (15).
  • the sensor calibration circuit 1600 includes the benefits associated with sensor calibration circuit 1100 and sensor calibration circuit 1300, as described.
  • a shutter can be added to supplement the described sensor readout circuits (e.g., sensor readout circuit 1000) to remove noises associated with sensor variation and l/f noise.
  • the shutter closes, temporarily shielding the active sensors from the sensor image.
  • Readout voltages of each column are measured when the shutter is closed.
  • the readout voltages measured while the shutter is closed can be denoted as Asj j (0).
  • the shutter opens, exposing the active sensors to the sensor image.
  • Readout voltages of each column are measured when the shutter is opened.
  • the readout voltages measured while the shutter is opened can be denoted as Asj j (t).
  • the impedance change caused by the sensor image (e.g., AZj j ) can be computed:
  • V biasi is the bias voltage associated with the reference sensor of the 1 th row (i.e., the currently selected row)
  • Zj j (t) is the absolute impedance of sensor (i,j) when Asj j (t) is measured (e.g., when the shutter is opened).
  • Shutter calibration can remove noise patterns due to sensor variation and reset l/f noise associated with the sensors and circuit elements.
  • sensor requirements determine the frequency of the shutter.
  • a sensor requirement is bolometer pixel noise equivalent temperature difference (NETD).
  • the described shutter calibration method is combined with the sensor calibration method associated with any of FIGS. 11, 13, 15, and 16.
  • the combination of the shutter calibration method and sensor calibration methods associated with FIGS. 15 and 16 is expressively described.
  • a person of ordinary skill in the art would recognize that computations associated with combinations of the calibration methods that are not explicitly disclosed can be easily derived from the disclosure and are within the scope of the disclosure.
  • the calibration quantities associated with the active sensors e.g., equation (15), D Sjj (0)
  • calibration sensor e.g., equation (20), Djyi(O)
  • equations (21) and (22) are combined to compute the quantity P y , which is associated with shutter calibration, the calibration sensor, and the calibration currents.
  • Equation (23) yields the term P y , which is substantially proportional to changes in the sensor image (i.e., change in active sensor impedance, D3 ⁇ 4).
  • the sensors are bolometers and the sensor image is incoming thermal radiation.
  • the combined shutter calibration, calibration sensor, and calibration current method utilizes one calibration current.
  • P y is substantially proportional to changes in the sensor image as follows:
  • FIG. 17 illustrates a method 1700 of sensor calibration, in accordance with an embodiment. In some embodiments, method 1700 is included in method 1400.
  • Method 1700 includes electrically uncoupling a readout element from a first calibration current source (step 1702).
  • a first calibration current source for example, referring to FIG. 16, the calibration current sources in calibration current circuit 1630 are electrically uncoupled from the readout elements in sensor readout circuit 1610.
  • the method 1700 includes electrically coupling a second readout element to the calibration current source (step 1704).
  • a second readout element For example, referring to FIG. 16, one of the calibration current sources in calibration current circuit 1630 is electrically coupled to the calibration readout element in calibration sensor circuit 1620.
  • the method 1700 includes measuring, with the second readout element, a third readout voltage caused by the calibration current (step 1706). For example, referring to FIG. 16, a readout voltage caused by the calibration current source is measured with the calibration readout element. [0433] The method 1700 includes electrically uncoupling the second readout element from the calibration current source (step 1708). For example, referring to FIG. 16, the calibration current sources in calibration current circuit 1630 is electrically uncoupled from the calibration readout element in calibration sensor circuit 1620.
  • the method 1700 includes electrically coupling a first terminal of a calibration sensor to a bias voltage node shared by a plurality of active sensors and the active sensor (step 1710).
  • the bias voltage node in sensor readout circuit 1610 is electrically coupled to the calibration sensor in calibration sensor circuit 1620.
  • the method 1700 includes electrically coupling a second terminal of the calibration sensor to the second readout element (step 1712).
  • the calibration sensor in calibration sensor circuit 1620 is electrically coupled to the calibration readout element in calibration sensor circuit 1620.
  • the method 1700 includes exposing a plurality of active sensors and the active sensor to a sensor image (step 1714). For example, referring to FIG. 16, the plurality of active sensors in sensor readout circuit 1610 is exposed to a sensor image.
  • the method 1700 includes shielding the calibration sensor from the sensor image (step 1716). For example, referring to FIG. 16, the calibration sensor in calibration sensor circuit 1620 is shielded from the sensor image.
  • the method 1700 includes measuring, with the second readout element, a fourth readout voltage of the calibration sensor (step 1718). For example, referring to FIG. 16, a readout voltage of the calibration sensor in calibration sensor circuit 1620 is measured with calibration readout element in calibration sensor circuit 1620.
  • the method 1700 includes computing a second output.
  • the output is based on the third readout voltage and the fourth readout voltage (step 1720).
  • D(t) associated with the calibration sensor column is computed based on the third and fourth readout voltages.
  • the method 1700 includes computing a difference.
  • the difference is between (1) the first output and (2) the second output weighted by a ratio between an impedance of the calibration sensor and an impedance of the active sensor (step 1722).
  • the term P y is computed based on the outputs D Sij (t) and D M (t).
  • FIG. 18A illustrates an exemplary sensor image. Due to pattern noises, horizontal noise patterns (an artifact of which is indicated with 1810) and vertical noise patterns (an artifact of which is indicated with 1820) are present in sensor image 1800.
  • FIG. 18B illustrates an exemplary sensor image after the disclosed calibration methods are used.
  • sensor image 1850 is free of the horizontal and vertical noise patterns that are observed in sensor image 1800.
  • Some MEMS systems utilize capacitive elements (e.g., sensors, capacitors) to store charge for readout.
  • capacitive elements e.g., sensors, capacitors
  • x-ray imaging systems can implement a two dimensional array of sensor pixels that either (1) directly convert x-ray photons to electrons or (2) utilize a scintillator plate to convert x-ray photons into visible photons which are then converted into photoelectrons by photodetectors that are sensitive to visible light.
  • the amount of electrons or photoelectrons incident on a sensor pixel can be represented by a charge stored in an equivalent capacitor (e.g., the junction capacitance in a photodiode, a pixel capacitor storing the photo-generated charge prior to readout).
  • a CTIA can include a high gain op-amp and a relatively large capacitor (e.g., 1-5 pF) to match the x-ray pixel capacitance. The high gain nature of the op-amp results in high power dissipation, which scales with the number of columns.
  • a sensor circuit includes a plurality of sensors each configured to store a charge, a Sigma-Delta ADC configured to receive the charge of each sensor, and a plurality of switches (each switch corresponding to a respective one of the plurality of sensors) configured to sequentially couple each of the plurality of sensors to the Sigma-Delta ADC.
  • the sensor circuit does not include a CTIA.
  • the sensor circuit does not include a CTIA electrically positioned between the plurality of sensor pixels and the Sigma- Delta ADC.
  • replacing a CTIA and an ADC with a Sigma-Delta ADC reduces the readout element’s power and area because the CTIA’s high-gain op-amp and large capacitor of the CTIA are no longer in the circuit.
  • Sigma-Delta ADCs replace CTIAs for all sensor columns, then the power and area reduction would be scaled by the number of sensor columns (see above— in some instances, an imaging system includes 3,000 columns), which can provide significant power and area savings without compromising sensitivity, resolution, or noise.
  • Reduction of power and area can reduce cost and increase reliability and portability of a system (e.g., an x-ray imaging system, a CMOS imaging system, a CCD imaging system) that includes the sensor circuit.
  • FIG. 19A illustrates an exemplary sensor circuit 1900.
  • the sensor circuit 1900 includes sensors 1902A-1902D, switches 1904A-1904D, and ADC 1906.
  • the ADC 1906 is a Sigma-Delta ADC that is configured to capture the charge of a selected sensor.
  • the discharge current from the selected sensor is a time-varying (e.g., exponentially decaying, step) signal.
  • the Sigma-Delta ADC is configured to receive the time- varying signal and capture substantively the total charge of the selected sensor.
  • a Sigma-Delta ADC can measure the total charge from the time-varying signal with sufficient resolution to satisfy accuracy requirements of a system.
  • a switch electrically couples a respective sensor to the Sigma-Delta ADC when a row of the respective sensor is selected (e.g., switch 1904A electrically couples sensor 1902A, which corresponds to a specific row, to the Sigma-Delta ADC).
  • switch 1904A electrically couples sensor 1902A, which corresponds to a specific row, to the Sigma-Delta ADC.
  • the sensor circuit does not include a CTIA electrically positioned between the plurality of sensors and the Sigma-Delta ADC.
  • Some embodiments include a method of manufacturing the circuit 1900.
  • the sensor circuit 1900 can be included in the described readout element in place of a CTIA.
  • readout element 102 or 1002 includes ADC 1906.
  • the capacitor symbols used to schematically represent the sensors are merely exemplary and not limiting.
  • the sensor 1902 is a sensor pixel.
  • the sensor 1902 is a sensor that receives radiation (e.g., X-ray) and converts the radiation into charge.
  • a charge is stored in a sensor pixel while the sensor pixel is sensing, and the capacitor is representative of the sensor pixel’s charge storing operation.
  • the sensor is an x-ray sensor photodiode, and the sensor accumulates charge in response to exposure to x-ray radiation; the total accumulated charge is representative of the x-ray radiation level and the capacitor symbol is used to represent the charge storing operation.
  • the sensor is an x-ray sensor pixel that directly converts x-ray photons into electrons and the electrons are stored in a capacitor (e.g., a pixel capacitor storing the photo-generated charge prior to readout).
  • the sensor circuit 1900 is merely exemplary.
  • the sensor circuit 1900 represents one column of sensors, and each sensor of the column belongs to a row (not shown) of sensors; each sensor of a column is readout at a different row time (e.g., during different discharge time windows).
  • a second sensor of the column is readout at a subsequent readout time using the same method described herein.
  • a first switch decouples a first sensor from the Sigma-Delta ADC and a second switch electrically couples a second sensor to the Sigma-Delta ADC during a second row time (e.g., a second discharge time window).
  • a Sigma-Delta ADC may be more suitable for receiving near- DC signals. Therefore, converting the discharge signal into a near-DC signal (e.g., a constant current) would be more desirable when including a Sigma-Delta ADC in a sensor circuit.
  • a CTIA and a sample-and-hold circuit may be included between the sensors and the Sigma- Delta ADC to generate a near DC input for Sigma-Delta analog-to-digital conversion. This may be particularly advantageous where a signal directly readout from a sensor includes high peaks and rapid transitions. If the signal includes sharp features, ADC resolution may be lost as the signal may not be adequately captured by the Sigma-Delta ADC.
  • adding a CTIA for each column of a sensor array can increase readout power and area of the readout chip.
  • FIG. 19B illustrates an exemplary sensor circuit 1950.
  • the sensor circuit 1950 includes sensors 1952A-1952D, switches 1954A-1954D, ADC 1956, variable resistor 1958, and control voltage 1960.
  • the ADC 1956 is a Sigma-Delta ADC that is configured to capture a total charge of a selected sensor.
  • the discharge current from the selected sensor is a time-varying (e.g., exponentially decaying, step) signal.
  • variable resistor is configured to receive the time-varying signal and output the total charge to the Sigma-Delta ADC.
  • the sensor circuit does not include a CTIA electrically positioned between the plurality of sensors and the Sigma-Delta ADC.
  • sensors 1952A-1952D correspond to sensors 1902A-1902D
  • switches 1954A-1954D correspond to switches 1904A-1904D
  • ADC 1956 correspond to ADC 1906.
  • elements similar to the ones described in FIG. 19A will not be described again.
  • Some embodiments include a method of manufacturing the circuit 1950.
  • the sensor circuit 1950 can be included in the described readout element in place of a CTIA.
  • readout element 102 or 1002 includes ADC 1956 and variable resistor 1958.
  • the variable resistor 1958 is electrically coupled to sensor 110, 112,
  • Variable resistor 1958 in front of Sigma-Delta ADC allows the discharge of a capacitor to be controlled during readout to reduce high peak amplitude and sharp features of an uncontrolled discharge signal.
  • the discharge signal can be controlled by varying the resistance of the variable resistor and matching a discharge time window with a row time of the readout operation.
  • a row time is when a row of sensors is readout.
  • variable resistor 1958 is implemented with a MOS transistor.
  • the resistance of the MOS transistor can be controlled with a control voltage 1960, which controls the transconductance of the transistor. It is understood that the transistor symbol is used to represent the variable resistor 1958 and the control voltage 1960 connected to the variable resistor are not limiting; other implementations of the variable resistor 1958 can exist without departing from the scope of the disclosure.
  • variable resistor 1958 is implemented with a weighted bank of resistors (not shown) in which discrete levels of resistance can be achieved (e.g., each combination between resistors of the weighted bank of resistors is unique).
  • the weighted bank of resistors includes a plurality of resistors that can be selectively electrically coupled in parallel or series and a plurality of corresponding switches.
  • each resistor has a unique value such that every different combination of resistors result in a different total resistance (e.g., the resistors’ values form a set of basis values that span a range of resistances from high to low in a stepwise manner (e.g., by increments of 50 ohms from 5.05 k-ohms to 5 ohms)).
  • the variable resistor 1958 is a MOS transistor.
  • the resistance of the variable resistor 1958 decreases from Ro.
  • T is 20 microseconds.
  • T is 40 microseconds.
  • T is between 10 microseconds and 1 millisecond.
  • the discharge time window is several magnitudes longer than a rise time of a signal turning on a comparable MOS transistor. Therefore, reducing a resistance of the variable resistor 1958 over the discharge time window may be different than merely turning on a transistor.
  • the discharge time window is in the microsecond range and a rise time of the signal turning on the MOS transistor is in nanosecond range.
  • the resistance of the variable resistor 1958 can be calculated as follows:
  • the control voltage 1960 is electrically coupled to the gate of the MOS transistor and increases the drain-to- source transconductance from low to high (i.e., resistance decreases from high to low) (e.g., by increasing the gate voltage) for each row time during readout.
  • variable resistor 1958 is implemented with a weighted bank of resistors (not shown) in which discrete levels of resistance can be achieved (e.g., each combination between resistors of the weighted bank of resistors is unique).
  • R(t) can be approximated with a stepwise function of the resistors of the weighted bank.
  • this resistance is the variable resistor’s lowest resistance.
  • the variable resistor is a MOS transistor, then the lowest resistance is determined by the conductance of the transistor (e.g., the transistor’s“on” resistance).
  • the variable resistor is a weighted bank of resistors, the lowest resistance is achieved by electrically coupling all the resistors of the bank in parallel.
  • the capacitance of the sensor 1902 can be represented with C.
  • the current going into the variable resistor 1958 can be calculated as follows:
  • the Ro of the variable resistor is determined by the effective capacitance (e.g., l-5pF) of the sensor 1902 and the discharge time window (e.g., row time).
  • variable resistor can be designed to convert the discharge current into a constant current.
  • the constant current By converting to the constant current using the sensor circuit 1950, resolution degradation due to high peak and/or sharp discharge signals being inputted to a Sigma-Delta ADC can be reduced without including a CTIA.
  • the term“constant current” is used in this example, it is understood that the converted current may include variations that do not substantively reduce the resolution of a Sigma-Delta ADC.
  • the charge of a sensor may not be completely readout.
  • the remaining charge may be discharged into the Sigma-Delta ADC with additional discharge paths.
  • the remaining charge may be ignored without substantively affecting ADC measurement.
  • the sensor circuit 1950 is merely exemplary.
  • the sensor circuit 1950 represents one column of sensors, and each sensor of the column belongs to a row of sensors; each sensor of a column is being readout at a different row time (e.g., at different discharge time windows).
  • a second sensor of the column is readout at a subsequent readout time using the same method described herein.
  • a second switch electrically couples a second sensor to the variable resistor during a second row time (e.g., a second discharge time window), and the current of the second sensor is converted to be near-DC for the Sigma-Delta ADC using the methods described herein.
  • the sensor circuit 1950 is described with one variable resistor, it is understood that a column of sensors can be associated with more than one variable resistor.
  • Ro can be adjusted in response to an updated row time requirement.
  • a weighted bank of resistors can be adjusted to set a different initial resistance.
  • initial resistance of the variable resistor can be adjusted before readout.
  • FIG. 20A illustrates an exemplary sensor circuit 2000.
  • the sensor circuit includes sensors 2002A-2002B and readout circuits 2004A-2004B.
  • the readout circuits include readout circuits 1900 or 1950. Because sensor circuit 2000 may not include a CTIA, the sensor circuit can enjoy the herein-described power, area, and resolution benefits.
  • the sensors 2002 are organized by N columns 2002A to 2002N. It is understood that“N” can be any number of columns.
  • “a column of sensors” is a plurality of sensors included in an array of sensors, arranged along a first dimension of the array, and bounded by boundaries of the array. Each sensor of the plurality sensors belongs to a unique row along a second dimension of the array.
  • the sensors 2002A and 2002B are spatially arranged by vertical columns of sensors (e.g., columns 2002A to 2002N).
  • a column of sensor is electrically coupled to the Sigma-Delta ADC in circuits 1900 and 1950.
  • readout circuit 2004A is configured to readout sensors 2002A
  • readout circuit 2004B is configured to readout sensors 2002B.
  • the sensors are x-ray sensor photodiodes and are part of an x-ray panel. In some embodiments, the sensors are part of a CMOS or CCD panel. In some embodiments, the readout circuits include Sigma-Delta ADCs. In some embodiments, the readout circuits do not include CTIA.
  • FIG. 20B illustrates an exemplary sensor circuit 2050.
  • the sensors 2052 are organized by N columns 2056A to 2056N.
  • the sensor circuit includes sensors 2052A-2052D and readout circuits 2054A-2054D.
  • the sensors are x- ray sensor photodiodes and are part of an x-ray panel having a same size as the panel described in FIG. 20A.
  • the sensors are part of a CMOS or CCD panel.
  • the sensors are arranged in columns, and each column includes a first plurality of sensors connected to a first readout circuit and a second plurality of sensors connected to a second readout circuit.
  • sensors 2052A includes the first plurality of sensors
  • sensor 2052B includes the second plurality of sensors
  • the combination of sensors 2052A and 2052B correspond to sensors 2002A described in FIG. 20A.
  • column 2056 A includes sensor from the first plurality of sensors and from the second plurality of sensors.
  • the panel is split - the first plurality of sensors includes a first half of the column sensors (as defined with respect to FIG. 20A), and the second plurality of sensors includes a second half of the column of sensors (e.g., the numbers of the first and second plurality of sensors are equal).
  • readout circuit 2004A is configured to readout sensors 2002A
  • readout circuit 2004B is configured to readout sensors 2002B
  • readout circuit 2004C is configured to readout sensors 2002C
  • readout circuit 2004D is configured to readout sensors 2004D.
  • a column is readout bi-directionally. For example, the first and second pluralities of sensors are readout at a same time with readout circuits 2004 A and 2004B.
  • the parasitic capacitance and resistance involved in the readout can be reduced.
  • the parasitic resistances and capacitances of column 2056A at the inputs of the respective readout circuits are each halved.
  • readout delays can be reduced.
  • row addressing complexity can be reduced. For example, the total row addresses are reduced because there are half as many rows to readout for each readout ASIC (compared the arrangement in FIG. 20A).
  • each of the readout circuits includes the sensor circuit 1900 or 1950 (for brevity, they will not be described again) and a Sigma-Delta ADC corresponding to each of the plurality of sensors.
  • the readout circuits do not include a CTIA.
  • the total readout circuits area and power dissipation in the architecture described in FIG. 20B can be less than a non- split column system including one CTIA per column.
  • parasitic capacitance of a column can range between 50-200 pF and parasitic resistance of a column can range between 1 kiloohm to 100 kiloohms; if a column is split into half as described herein, the parasitic values would respectively be reduced by a factor of two.
  • FIGS. 21A-21D and table 1 show simulation results of the Sigma-Delta ADC, demonstrating conversion of time varying signals during a time period.
  • Table 1 shows Effective Number of Bits (ENOB) as a function of Over Sampling Rate (OSR) and the input signal shapes described with respect to FIGS. 21A-21D.
  • ENOB Effective Number of Bits
  • OSR Over Sampling Rate
  • the curve in FIG. 21A shows random ideal constant inputs which generate the ENOB shown in Table 1.
  • the curve in FIG. 21B shows a current clamped signal; a current clamp on a column forces a current inputted to the ADC to be constant until the charge is completely depleted, effectively creating pulse-width modulated inputs.
  • the curve in FIG. 21C is an exponentially decaying signal that has a length of two RC time constants. In some embodiments, if the charge is not yet fully depleted after two time constants, a low resistance switch is used to discharge the remaining charge into the ADC.
  • the curve in FIG. 21D is an exponentially decaying signal that has a length of five RC time constants.
  • the ENOB is reduced compared to the two time constant signal.
  • the curves illustrated in FIGS. 21C and 21D are representative of a sensor readout charge signal (e.g., a sensor’s total charge is discharged into the ADC). It is understood that the curves are presented for illustrative purposes and are not necessarily drawn to scale.
  • a digital filter is used with the Sigma-Delta ADC to improve performance.
  • the digital filter is used to process digital signals outputted from circuit 1900 or 1950.
  • the digital filter is a Finite Impulse Response (FIR) filter.
  • the coefficients of the Finite Impulse Response (FIR) filter can be chosen to reduce quantization error and increase linearity.
  • FIR filter for the current clamped waveform (e.g., FIG. 21B), a FIR filter with the same value for all coefficients (e.g., a rectangular window) can be used to improve performance.
  • a Blackman or Hamming window can be used for the FIR filter to improve performance.
  • a CEP (cyclic excitation process) effect is implemented on amorphous-Silicon.
  • This may increase the sensitivity of the sensor pixel.
  • an x- ray sensor pixel can be manufactured with an amorphous Si based nip (n-type/intrinsic/p- type) structure for indirect detection or an x-ray sensitive photoconductor (e.g., Selenium) with electrode structures to allow for photoelectrons to be addressed.
  • an x-ray sensitive photoconductor e.g., Selenium
  • producing internal gain for the photoexcited (primary) charged carriers can reduce the x-ray radiation levels required to produce detectable signals.
  • CEP produces high gain without the high electric fields (as may be the case for conventional avalanche multiplication effects).
  • CEP devices can be used in for x-ray indirect detection.
  • CEP devices can be used in for x-ray indirect detection.
  • CEP effect is harnessed in conjunction with x-ray photoconductors such as selenium.
  • FIG. 22 illustrates a method 2200 of manufacturing an electromechanical system, in accordance with an embodiment.
  • the electrochemical system could be associated with circuits 100, 300, 500, 600, 800, 900, 1000, 1100, 1300, 1500, 1600, 1900, 1950, 2000, and 2050 (and related methods).
  • To manufacture an electromechanical system all or some of the process steps in method 2200 could be used and used in a different order.
  • Step 2214 could be performed before Step 2212.
  • Method 2200 includes Step 2202, providing a substrate.
  • the substrate is made of glass.
  • the substrate is low temperature polycrystalline silicon.
  • the substrate is a borosilicate that contains additional elements to fine tune properties.
  • An example of a borosilicate is by Corning EagleTM, which produces an alkaline earth boro aluminosilicate (a silicate loaded with boron, aluminum, and various alkaline earth elements). Other variations are available from Asahi GlassTM or SchottTM.
  • a flat panel glass process is used to manufacture the electromechanical system.
  • a liquid crystal display (LCD) process is used to manufacture the electromechanical system.
  • an OLED display process or an x-ray panel process is used.
  • Employing a flat panel glass process may allow for increased substrate sizes, thereby allowing for a higher number of electrochemical systems per substrate, which reduces processing costs.“Panel level” sizes can include 620 mm x 750mm, 680 mm x 880 mm, 1100 mm x 1300 mm, 1300 mm x 1500 mm, 1500 mm x 1850 mm, 1950 mm x 2250 mm, and 2200 mm x 2500 mm.
  • thin film transistors (TFTs) in panel level manufacturing can also reduce cost and so, for example, LCD-TFT processes can be beneficial.
  • Method 2200 includes Step 2204, adding MEMS to the substrate.
  • MEMS is used to describe the addition of structures, it should be appreciated that other structures could be added without deviating from the scope of this disclosure.
  • the MEMS structures may be added using an LCD-TFT process.
  • Step 2204 may be followed by optional Step 2216, sub-plating.
  • Step 2216 may be used when the substrate is larger than the processing equipment used in subsequent steps.
  • Step 2204 cutting the panel into wafer sizes to perform further processing (using, for example, CMOS manufacturing equipment).
  • the same size substrate is used throughout method 2200 (i.e., Step 2216 is not used).
  • Method 2200 includes Step 2206, releasing the MEMS from the substrate.
  • Method 2200 includes Step 2208, post-release processing.
  • Such post-release processing may prepare the MEMS structure for further process steps, such as planarization.
  • planarization can include chemical mechanical planarization.
  • the further process steps include etch back, where a photoresist is spun onto the topography to generate a more planar surface, which is then etched. Higher control of the etch time can yield a smoother surface profile.
  • the further process steps include“spin on glass,” where glass-loaded organic binder is spun onto the topography and the result is baked to drive off organic solvents, leaving behind a surface that is smoother.
  • Method 2200 includes Step 2210, vacuum encapsulation of the MEMS structure, where necessary. Vacuum encapsulation may be beneficial to prolong device life.
  • Method 2200 includes Step 2212, singulation. Some embodiments may include calibration and chip programming, which may take into account the properties of the sensors. Methods described herein may be advantageous in glass substrate manufacturing processes because uniformity in glass lithography capabilities is limited. As a further advantage, glass has a lower thermal conductivity and so a glass substrate can be a better thermal insulator; by manufacturing thin structures separating a bolometer pixel from a glass substrate,
  • embodiments herein may better serve to thermally isolate the glass bolometer pixel from the packaging environment.
  • Method 2200 includes Step 2214, attachment of a readout integrated circuit (ROIC) and flex/PCB attachment.
  • the readout circuits could be associated with circuits 100, 300, 500, 600, 800, 900, 1000, 1100, 1300, 1500, 1600, 1900, 1950, 2000, and 2050 (and related methods).
  • Processes and devices described herein may have the further advantage that the area required for signal processing can be much smaller than the sensing area which is dictated by the sensing physics.
  • sensors are integrated on top of CMOS circuitry, and area driven costs lead to a technology node that is not optimal for the signal processing task.
  • the ROIC is specifically designed for sensing a specific electromagnetic wavelength (such as X-Rays, THz, LWIR).
  • FIG. 23 illustrates an exemplary sensor.
  • sensor 2300 is manufactured using method 2200.
  • Sensor 2300 includes glass substrate 2306, structure 2304 less than 250 nm wide coupled to glass substrate 2306, and a sensor pixel 2302 coupled to the structure 2304.
  • structure 2304 is a hinge that thermally separates the active area from the glass.
  • sensor 2300 receives an input current or charge and outputs an output current or charge based on the received radiation (e.g., the resistance between two terminals of the sensor changes in response to exposure to LWIR radiation).
  • a sensor includes a glass substrate, a structure
  • a sensor includes a MEMS or NEMS device manufactured by a LCD-TFT manufacturing process and a structure manufactured by any of the methods described herein.
  • sensors can include resistive sensors and capacitive sensors.
  • Bolometers can be used in a variety of applications.
  • long wave infra-red (LWIR, wavelength of approximately 8-14 pm) bolometers can be used in the automotive and commercial security industries.
  • Terahertz (THz, wavelength of approximately 1.0-0.1 mm) bolometers can be used in security (e.g., airport passenger security screening) and medical (medical imaging).
  • Some electrochemical systems can include X-Ray sensors or camera systems.
  • LWIR and THz sensors are used in camera systems.
  • Some electromechanical systems are applied in medical imaging, such as endoscopes and exoscopes.
  • X-ray sensors include direct and indirect sensing configurations.
  • Electromechanical systems include scanners for light detection and ranging (LIDAR) systems. For example, optical scanners where spatial properties of a laser beam could be shaped (for, e.g., beam pointing).
  • Electromechanical systems include inertial sensors (e.g., where the input stimulus is linear or angular motion). Some systems may be used in bio sensing and bio therapeutic platforms (e.g., where biochemical agents are detected).
  • a sensor readout circuit includes a readout element, a first current source, a second current source, a voltage driver, a reference sensor, and an active sensor.
  • the readout element includes an input.
  • the voltage driver includes an output.
  • the reference sensor includes a first terminal and a second terminal; the first terminal is electrically coupled to the first current source and the second terminal is electrically coupled to the output of the voltage driver.
  • the active sensor includes a first terminal and a second terminal; the first terminal is electrically coupled to the second current source and the input of the readout element and the second terminal is electrically coupled to the output of the voltage driver.
  • the active sensor is configured for exposure to a sensor image.
  • the first current and the second current are constant.
  • the voltage driver generates a bias voltage for the active sensor.
  • the active sensor is further configured to change a current from the first terminal of the active sensor to the input of the readout element when the active sensor is exposed to the sensor image.
  • the active sensor is further configured to change an impedance of the active sensor when the active sensor is exposed to the sensor image.
  • the reference sensor is a reference bolometer pixel and the active sensor is an active bolometer pixel.
  • the circuit further includes a second reference sensor, a second active sensor, a first switch, a second switch, a third switch, and a fourth switch.
  • the second reference sensor includes a first terminal and a second terminal; the first terminal is electrically coupled to the first current source and the second terminal is electrically coupled to the voltage driver.
  • the second active sensor includes a first terminal and a second terminal; the first terminal is electrically coupled to the second current source outputting the second current and the second terminal is electrically coupled to the output of the voltage driver.
  • the second active sensor is configured to change the current from the first terminal to the input of the readout element.
  • the first switch is configured to selectively electrically couple the reference sensor to the first current source.
  • the second switch is configured to selectively electrically couple the active sensor to the second source.
  • the third switch is configured to selectively electrically couple the second reference sensor to the first current source.
  • the fourth switch is configured to selectively electrically couple the second active sensor to the second current source.
  • the circuit further includes a CDS circuit that is configured to remove an offset.
  • the voltage of the readout element is proportional to an impedance difference between the reference sensor and the active sensor.
  • the circuit further includes an output of an op amp electrically coupled to the second terminal of the reference sensor.
  • the circuit further includes a feedback element that is electrically coupled to the first and second terminals of the reference sensor.
  • the circuit further includes a third reference sensor and a third current source.
  • the third reference sensor includes a first terminal and a second terminal that is electrically coupled to the output of the voltage driver.
  • the third current source is electrically coupled to the first terminal of the third reference sensor, and is configured to output a seventh current reflective of self-heating generated by the third reference sensor. The value of the second current adjusts in accordance with the seventh current.
  • the circuit further includes an ADC that is configured to sample the change of the current from the first terminal to the input of the readout element.
  • the first current source and the second current source that are configured to output an equal magnitude of current in a same direction relative to the respective first terminals.
  • the readout element includes a CTIA.
  • the first current source and the second current source are selected from the group of an athermal voltage source and resistor, a high-impedance athermal transistor current source, and a Wilson current mirror.
  • the circuit further includes an amplifier that outputs to the second terminal of the reference sensor.
  • the first terminal of the reference sensor electrically couples to a negative input of the amplifier.
  • the first current source is configured to generate a voltage drop across the negative input and the output.
  • the reference sensor is a reference bolometer pixel
  • the active sensor is a bolometer pixel configured to detect LWIR radiation.
  • the readout element includes a Sigma-Delta ADC.
  • a first stage of the Sigma-Delta ADC includes a CTIA.
  • the reference sensor is shielded from a sensor image.
  • the circuit further includes a voltage follower electrically coupled between the output of the voltage driver and the second terminal of the active sensor.
  • the circuit further includes two or more current buffers, the two or more current buffers including a first current buffer electrically coupled between the first current source and the reference sensor and a second current buffer electrically coupled between the second current source and the active sensor.
  • a method of sensor readout includes: providing a first current to a first terminal of a reference sensor; generating, from the first current, a voltage at a second terminal of the reference sensor; providing a second current to a first terminal of the active sensor; driving, at the voltage, a second terminal of an active sensor; exposing the active sensor to a sensor image; and measuring a third current from the first terminal of the active sensor to an input of a readout element.
  • the first current and the second current are constant.
  • the voltage is a bias voltage for the active sensor.
  • exposing the active sensor to the sensor image further includes changing the third current.
  • exposing the active sensor to the sensor image further includes changing an impedance of the active sensor.
  • the method further includes:
  • the method includes: electrically uncoupling, from the reference sensor, a first current source providing the first current;
  • the method further includes:
  • a voltage at an output of the readout element is proportional to an impedance difference between the reference sensor and the active sensor.
  • the voltage is driven by an op amp, and the first terminal of the reference sensor is electrically coupled to a negative input of the op amp.
  • the method further includes feeding back from the second terminal of the reference sensor to the first terminal of the reference sensor using a feedback element.
  • the method further includes:
  • the method further includes sampling a voltage generated by the current to the input of a readout element.
  • the first current and the second current are equal in magnitude and in a same direction relative to the respective first terminals of the reference sensor and active sensor.
  • the method further includes converting the third current to a readout voltage of the readout element.
  • the first current and the second current are each provided by current sources selected from the group of an athermal voltage source and resistor, a high-impedance athermal transistor current source, and a Wilson current mirror.
  • driving the second terminal of the active sensor at the voltage further includes driving, from an output of a voltage driver, the second terminal of the reference sensor and the second terminal of the active sensor.
  • the method further includes causing a voltage drop across the reference sensor from the first current; generating the voltage using an amplifier outputting to the second terminal of the reference sensor; and electrically coupling the first terminal of the reference sensor to a negative terminal of the amplifier.
  • the reference sensor is a reference bolometer pixel and the active sensor is an active bolometer pixel.
  • exposing the active sensor to the sensor image further includes exposing the active sensor to LWIR radiation.
  • the readout element includes a Sigma-Delta ADC.
  • a first stage of the Sigma-Delta ADC includes a CTIA.
  • the method further includes exposing the reference sensor to an ambient condition common to the reference sensor and active sensor; and shielding the reference sensor from the sensor image.
  • driving the second terminal of the active sensor at the voltage further includes buffering between the second terminal of the active sensor and a voltage source providing the voltage.
  • the method further includes:
  • a method of manufacturing a sensor readout circuit includes providing a readout element including an input; providing a first current source; providing a second current source; providing a voltage driver including an output; providing a reference sensor including a first terminal and a second terminal; electrically coupling the first terminal of the reference sensor to the first current source; electrically coupling the second terminal of the reference sensor to the output of the voltage driver; providing an active sensor including a first terminal and a second terminal, the active sensor configured for exposure to a sensor image; electrically coupling the first terminal of the active sensor to the second current source and the input of the readout element; and electrically coupling the second terminal of the active sensor to the output of the voltage driver.
  • the first current and the second current sources are constant current sources.
  • the voltage driver is configured to generate a bias voltage for the active sensor.
  • the active sensor is further configured to change a current from the first terminal of the active sensor to the input of the readout element when the active sensor is exposed to the sensor image.
  • the active sensor is further configured to change an impedance of the active sensor when the active sensor is exposed to the sensor image.
  • the reference sensor is a reference bolometer pixel and the active sensor is an active bolometer pixel.
  • the method of manufacturing further includes: providing a second reference sensor including a first terminal and a second terminal; electrically coupling the first terminal of the second reference sensor to the first current source; electrically coupling the second terminal of the second reference sensor to the voltage driver; providing a second active sensor including a first terminal and a second terminal, the second active sensor configured for exposure to the sensor image;
  • the second active sensor is configured to change a current from the first terminal of the active sensor to the input of the readout element; and providing a first switch configured to selectively electrically couple the reference sensor to the first current source; providing a second switch configured to selectively electrically couple the active sensor to the second current source; providing a third switch configured to selectively electrically couple the second reference sensor to the first current source; and providing a fourth switch configured to selectively electrically couple the second active sensor to the second current source.
  • the method of manufacturing further includes providing a CDS circuit configured to remove an offset.
  • the readout element is configured to generate a voltage proportional to an impedance difference between the reference sensor and the active sensor.
  • the method of manufacturing further includes: providing an op amp; and electrically coupling an output of an op amp to the second terminal of the reference sensor.
  • the method of manufacturing further includes: providing a feedback element; and electrically coupling the feedback element to the first and second terminals of the reference sensor.
  • the method of manufacturing further includes: providing a third reference sensor including a first terminal and a second terminal; electrically coupling the second terminal of the third reference sensor to the output of the voltage driver; providing a third current source configured to output a seventh current reflective of self-heating generated by the third reference sensor, where a value of the second current adjusts in accordance with the seventh current; and electrically coupling the third current source to the first terminal of the third reference sensor.
  • the method of manufacturing further includes providing an ADC configured to sample the change of the current from the first terminal to the input of the readout element.
  • the first current source and the second current source are configured to output an equal magnitude of current in a same direction relative to the respective first terminals.
  • the readout element includes a CTIA.
  • the first current source and the second current source are selected from the group of an athermal voltage source and resistor, a high-impedance athermal transistor current source, and a Wilson current mirror.
  • the method of manufacturing further includes: providing an amplifier outputting to the second terminal of the reference sensor; and electrically coupling the first terminal of the reference sensor to a negative input of the amplifier, where the first current source is configured to generate a voltage drop across the negative input and the output.
  • the reference sensor is a reference bolometer pixel and the active sensor is a bolometer pixel configured to detect LWIR radiation.
  • the readout element includes a Sigma-Delta ADC.
  • a first stage of the Sigma- Delta ADC includes a CTIA.
  • the reference sensor is shielded from a sensor image.
  • the method of manufacturing further includes: providing a voltage follower; and electrically coupling the voltage follower between the output of the voltage driver and the second terminal of the active sensor.
  • the method of manufacturing further includes: providing two or more current buffers including a first current buffer and a second current buffer; electrically coupling the first current buffer between the first current source and the reference sensor; and electrically coupling the second current buffer between the second current source and the active sensor.
  • a sensor circuit includes: a plurality of active sensors exposed to a sensor image and sharing a bias voltage node; a calibration readout element; and a calibration sensor shielded from the sensor image and including a first terminal electrically coupled to the bias voltage node and a second terminal electrically coupled to the calibration readout element.
  • an impedance of the calibration sensor is the same as an impedance of an active sensor of the plurality of active sensors, and where an electrical carrier count of the calibration sensor is greater than an electrical carrier count of the active sensor.
  • the sensor circuit further includes: a readout element corresponding to an active sensor of the plurality of active sensors and configured to measure a readout voltage of the active sensor, where the calibration readout element is configured to measure a readout voltage of the calibration sensor, and the sensor circuit is electrically coupled to: a processor; and a memory including instructions, which when executed by the processor, cause the processor to perform a method that includes: receiving the readout voltage of the active sensor; receiving the readout voltage of the calibration sensor; and computing a difference between (1) the readout voltage of the active sensor and (2) the readout voltage of the calibration sensor weighted by a ratio between an impedance of the calibration sensor and an impedance of the active sensor.
  • the ratio is one.
  • the ratio is temperature independent.
  • the sensor circuit further includes: a readout element corresponding to an active sensor of the plurality of active sensors and configured to measure a readout voltage of the active sensor, where the sensor circuit is electrically coupled to: a processor; and a memory including instructions, which when executed by the processor, cause the one or more processors to perform a method that includes: receiving a first readout voltage corresponding to a closed shutter; receiving a second readout voltage corresponding to an opened shutter; and computing a difference proportional to an impedance difference of the active sensor caused by the sensor image between (1) the first readout voltage and (2) the second readout voltage.
  • the plurality of readout elements includes a plurality of ADCs.
  • the calibration sensor and the plurality of active sensors are made from materials having a same thermal coefficient of resistance (TCR).
  • the plurality of active sensors includes a plurality of columns of active sensors
  • the circuit further includes: a plurality of current sources, where a current source of the plurality of current sources is electrically coupled to the second terminal of the calibration sensor and the calibration readout element; and a plurality of readout elements, where each of the plurality of columns of active sensors is electrically coupled to: a corresponding current source of the plurality of current sources at a corresponding readout node, and a corresponding readout element of the plurality of readout elements at the corresponding readout node.
  • the calibration readout element includes an analog-to-digital converter (ADC).
  • ADC analog-to-digital converter
  • the plurality of active sensors and the calibration sensor are bolometers, and the sensor image is a thermal image.
  • a sensor circuit includes: a calibration current source providing a calibration current; an active sensor; a readout element; a first switch configured to selectively electrically couple the active sensor to the readout element; and a second switch configured to selectively electrically couple the calibration current source to the readout element.
  • the second switch is configured to electrically uncouple the calibration current source from the first readout element when the first switch electrically couples the active sensor to the readout element
  • the first switch is configured to electrically uncouple the active sensor from the first readout element when the second switch electrically couples the calibration current to the readout element
  • the sensor circuit is electrically coupled to: a processor; and a memory including instructions, which when executed by the processor, cause the processor to perform a method including: receiving a first readout voltage of the active sensor; receiving a second readout voltage caused by the calibration current; and computing an output proportional to a readout current of the active sensor based on (1) the first readout voltage and (2) the second readout voltage.
  • the sensor circuit further includes: a plurality of active sensors including the active sensor; and a plurality of readout elements including the first and second readout elements, each of the plurality of readout elements electrically coupled to a respective active sensor of the plurality of active sensors, where the method further includes: receiving, from a readout element of the plurality of readout elements, a first readout voltage of the respective active sensor; receiving a second readout voltage caused by the calibration current on a respective readout element; and computing a respective output proportional to a readout current of the respective active sensor based on (1) the readout voltage of the respective sensor and (2) the second readout voltage caused by the calibration current on the respective readout element.
  • the sensor circuit further includes a second active sensor belonging to a same column as the first active sensor, where the method further includes, after computing the first output: receiving a third readout voltage of the second active sensor; and computing a second output proportional to a readout current of the fourth active sensor based on (1) the third readout voltage and (2) the second readout voltage caused by the calibration current.
  • a time between successive receipts of the second readout voltage on the same column caused by the calibration current is a calibration period.
  • the calibration period is one second.
  • the calibration period is based on a drift of the readout element.
  • the sensor circuit further includes: a second calibration current source; a third switch configured to selectively electrically couple the first calibration current source to the readout element; and a fourth switch configured to selectively electrically couple the second calibration current source to the readout element, and where when the third switch electrically uncouples the readout element from the first calibration current source: the fourth switch is configured to electrically couple the readout element to the second calibration current source, and the method further includes receiving a third readout voltage caused by the second calibration current; and the output is further based on the third readout voltage caused by the second calibration current.
  • the readout element includes an ADC.
  • the sensor circuit is electrically coupled to: a processor; and a memory including instructions, which when executed by the processor, cause the one or more processors to perform a method that includes: receiving a first readout voltage corresponding to a closed shutter; receiving a second readout voltage corresponding to an opened shutter; and computing a difference proportional to an impedance difference of the first active sensor caused by a sensor image between (1) the first readout voltage and (2) the second readout voltage.
  • the active sensor is a bolometer exposed to a thermal scene.
  • the active sensor is exposed to a sensor image and shares a bias voltage node with a plurality of active sensors
  • the sensor circuit further includes: a second readout element; and a calibration sensor shielded from the sensor image and including a first terminal electrically coupled to the bias voltage node and a second terminal electrically coupled to the second readout element.
  • a method of calculating a calibrated voltage in a sensor circuit includes: electrically coupling a first terminal of a calibration sensor to a bias voltage node shared by a plurality of active sensors; electrically coupling a second terminal of the calibration sensor to a calibration readout element; exposing the plurality of active sensors to a sensor image; shielding the calibration sensor from the sensor image; measuring, with a readout element, a readout voltage of an active sensor of the plurality of active sensors; measuring, with the calibration readout element, a readout voltage of the calibration sensor; and computing the calibrated voltage as a difference between (1) the readout voltage of the active sensor and (2) the readout voltage of the calibration sensor weighted by a ratio between an impedance of the calibration sensor and an impedance of the active sensor.
  • the impedance of the calibration sensor is the same as the impedance of the active sensor, and where an electrical carrier count of the calibration sensor is greater than an electrical carrier count of the active sensor.
  • the ratio is one.
  • the ratio is temperature independent.
  • the calibration sensor and the active sensor are made from materials having a same TCR.
  • the method further includes: electrically coupling a current source of a plurality of current sources to the second terminal of the calibration sensor and to the calibration readout element; electrically coupling a column of a plurality of columns of active sensors to the readout element, the column of active sensors including the active sensor; and electrically coupling a second current source of the plurality of current sources to the readout element.
  • the method further includes: closing a shutter; measuring, with the readout element, a first readout voltage corresponding to the closed shutter; and measuring, with the calibration readout element, a second readout voltage corresponding to the closed shutter; and after computing the calibrated voltage, computing a second difference between (1) the calibrated voltage and a difference between (2a) the first readout voltage and (2b) the second readout voltage weighted by the ratio, where the second difference is a shutter calibrated voltage.
  • the calibration readout element includes an ADC.
  • the readout element includes an ADC.
  • the plurality of active sensors and the calibration sensor are bolometers, and the sensor image is a thermal image.
  • Some aspects include a method of manufacturing the above circuits.
  • a method of calculating an output in a sensor circuit includes: electrically coupling a readout element to an active sensor; measuring, with the readout element, a first readout voltage of the active sensor; electrically uncoupling the readout element from the active sensor; electrically coupling a calibration current to the readout element; measuring, with the readout element, a second readout voltage caused by the calibration current; and computing the output based on (1) the first readout voltage and (2) the second readout voltage, the output proportional to a readout current of the active sensor.
  • the method further includes: electrically coupling a respective active sensor of a plurality of active sensors to a readout element of a plurality of readout elements; measuring, with the respective readout element, a first readout voltage of the respective active sensor; electrically uncoupling the respective readout element from the respective active sensor; electrically coupling the calibration current to the respective readout element; measuring, with the respective readout element, a second readout voltage caused by the calibration current on the respective readout element; and computing an output proportional to a readout current of the respective active sensor based on (1) the first readout voltage of the respective active sensor and (2) the second readout voltage caused by the calibration current.
  • the method further includes, after computing the first output: electrically uncoupling the calibration current source from the readout element; electrically coupling the readout element to a second active sensor, the second active sensor belonging to a same column as the first active sensor; measuring, with the readout element, a third readout voltage of the second active sensor; and computing a second output proportional to a readout current of the second active sensor based on (1) the third readout voltage and (2) the second readout voltage caused by the calibration current.
  • a time between successive measurements of the second readout voltage on the same column caused by the calibration current is a calibration period.
  • the calibration period is one second.
  • the calibration period is based on a drift of the readout element.
  • the method further includes: electrically uncoupling the readout element from the first calibration current source; electrically coupling the readout element to a second calibration current source; and measuring, with the readout element, a third readout voltage caused by the second calibration current on the readout element, where the output is further based on the third readout voltage caused by the second calibration current.
  • the readout element includes an ADC.
  • the method further includes: closing a shutter; computing the output corresponding to a closed shutter; and computing a difference proportional to an impedance difference of the active sensor caused by a sensor image between (1) the output corresponding to an opened shutter and (2) the output corresponding to the closed shutter.
  • the active sensor is a bolometer exposed to a thermal scene.
  • the method further includes: electrically uncoupling the readout element from the calibration current source; electrically coupling a second readout element to the calibration current source; measuring, with the second readout element, a third readout voltage caused by the calibration current; electrically uncoupling the second readout element from the calibration current source; electrically coupling a first terminal of a calibration sensor to a bias voltage node shared by a plurality of active sensors and the active sensor; electrically coupling a second terminal of the calibration sensor to the second readout element; exposing the plurality of active sensors and the active sensor to a sensor image; shielding the calibration sensor from the sensor image; measuring, with the second readout element, a fourth readout voltage of the calibration sensor; computing a second output based on the third readout voltage and the fourth readout voltage; and computing a difference between (1) the first output and (2) the second output weighted by a ratio between an impedance of the calibration sensor and an impedance of the active sensor.
  • a sensor circuit includes: a plurality of sensor pixels, each configured to store a charge; a Sigma-Delta ADC configured to receive the charge of each sensor; and a plurality of switches configured to sequentially couple each of the plurality of sensor pixels to the Sigma-Delta ADC, each switch corresponding to a respective one of the plurality of sensor pixels.
  • the sensor circuit does not include a CTIA electrically positioned between the plurality of sensor pixels and the Sigma-Delta ADC.
  • the sensor circuit further includes a variable resistor electrically positioned between the plurality of sensors and the Sigma-Delta ADC, wherein the plurality of switches are configured to sequentially couple each of the plurality of sensor pixels to the variable resistor.
  • the variable resistor has a linearly decreasing resistance during a discharge time window; the variable resistor is at a lowest resistance at an end of the discharge time window; and the variable resistor has a resistance higher than the lowest resistance between the beginning and the end of the discharge time window.
  • variable resistor is a MOS transistor; and the initial resistance, the linearly decreasing resistance, and the lowest resistance of the MOS transistor are controlled with a control voltage electrically coupled to the MOS transistor.
  • the discharge time window is between 10 microseconds and 1 millisecond.
  • a first switch electrically couples a first sensor pixel and the Sigma-Delta ADC; during a second discharge time window, a second switch electrically couples a second sensor pixel and the Sigma-Delta ADC; and the first and second discharge time windows correspond to readout times of the first and second sensor pixels.
  • a constant current of the variable resistor is an initial voltage of the variable resistor divided by the initial resistance.
  • a switch electrically couples a respective sensor pixel and the variable resistor during a respective discharge time window, the discharge time window equal to a capacitance of the sensor pixel multiplied by an initial resistance of the variable resistor.
  • the variable resistor includes a weighted bank of resistors; the weighted bank of resistors include a plurality of resistors selectively electrically coupled in parallel or in series; and resistances of combinations of the selective electrically coupled resistors include an initial resistance at the beginning of a discharge time window, a linearly decreasing resistance, and a lowest resistance.
  • a sensor pixel includes an x-ray sensor photodiode and the charge is indicative of the x-ray sensor photodiode’s exposure to x-ray.
  • a sensor pixel includes a storage capacitor storing the charge and the sensor pixel’s exposure to x-ray generates the charge stored in the storage capacitor.
  • the sensor circuit further includes a second plurality of sensor pixels and a second Sigma-Delta ADC, wherein the second plurality of sensor pixels are configured to sequentially couple to the second Sigma-Delta ADC and the first and second pluralities of sensor pixels belong to a same column.
  • numbers of the first and second plurality of sensor pixels are equal.
  • a first sensor pixel of the first plurality of sensor pixels and a second sensor pixel of the second plurality of sensor pixels are simultaneously readout.
  • an input current to the Sigma-Delta ADC is constant.
  • the sensor circuit further includes a digital filter configured to receive a signal from the Sigma-Delta ADC.
  • a sensor circuit includes a plurality of sensor pixels, a Sigma-Delta ADC, and a plurality of switches, each switch corresponding to a respective one of the plurality of sensor pixels; a method of readout of the sensor circuit includes: storing respective charges in each of the plurality of sensor pixels; sequentially electrically coupling, using the plurality of switches, each of the plurality of sensor pixels to the Sigma-Delta ADC; and sequentially receiving, at the Sigma-Delta ADC, the respective charge of each sensor pixel.
  • the sensor circuit does not include a CTIA electrically positioned between the plurality of sensor pixels and the Sigma-Delta ADC and the respective charge of each sensor pixel is not received by the CTIA.
  • the sensor circuit further includes a variable resistor electrically positioned between the plurality of sensor pixels and the Sigma- Delta ADC and the method further includes sequentially electrically coupling, using the plurality of switches, each of the plurality of sensor pixels to the Sigma-Delta ADC further includes sequentially electrically coupling, using the plurality of switches, the each of the plurality of sensor pixels to the variable resistor.
  • the method further includes linearly decreasing a resistance of the variable resistor during a discharge time window, wherein: the variable resistor is at a lowest resistance at an end of the discharge time window; and the variable resistor has a resistance higher than the lowest resistance between the beginning and the end of the discharge time window.
  • variable resistor is a MOS transistor electrically coupled to a control voltage and linearly decreasing the resistance of the variable resistor further includes driving the MOS transistor with the control voltage to generate the initial resistance, the linearly decreasing resistance, and the lowest resistance.
  • the discharge time window is between 10 microseconds and 1 millisecond.
  • sequentially electrically coupling, using the plurality of switches, each of the plurality of sensor pixels to the Sigma-Delta ADC further includes: during the first discharge time window, electrically coupling a first switch to a first sensor pixel and the Sigma-Delta ADC; during a second discharge time window, electrically coupling a second switch to a second sensor pixel and the Sigma-Delta ADC, wherein the first and second discharge time windows correspond to readout times of the first and second sensor pixels.
  • a constant current of the variable resistor is an initial voltage of the variable resistor divided by the initial resistance.
  • sequentially electrically coupling, using the plurality of switches, each of the plurality of sensor pixels to the Sigma-Delta ADC further includes electrically coupling a switch to a respective sensor pixel and the variable resistor during a respective discharge time window; and the discharge time window is equal to a capacitance of the sensor pixel multiplied by an initial resistance of the variable resistor.
  • the variable resistor includes a weighted bank of resistors; the weighted bank of resistors include a plurality of resistors selectively electrically coupled in parallel or in series; and the method further includes linearly decreasing resistances of combinations of the plurality of resistors, from an initial resistance at a beginning of a discharge time window to a lowest resistance at an end of the discharge time window, by selective electrically coupling the resistors.
  • a sensor pixel includes an x-ray sensor photodiode and the charge is indicative of the x-ray sensor photodiode’s exposure to x-ray.
  • storing respective charges in each of the plurality of sensor pixels further includes: exposing the each of the plurality of sensor pixels to x-ray and generating the respective charge; and storing the respective charges in a storage capacitor of the each of the plurality of sensor pixels.
  • the sensor circuit further includes a second plurality of sensor pixels belonging to a same column as the first plurality of sensor pixels, a second plurality of switches, and a second Sigma-Delta ADC
  • the method further includes: sequentially electrically coupling, using the second plurality of switches, each of the plurality of sensor pixels to the second Sigma-Delta ADC; and sequentially receiving, at the second Sigma-Delta ADC, the respective charge of each sensor pixel of the second plurality of sensor pixels.
  • the first Sigma-Delta ADC receives a first respective charge of a first sensor pixel of the first plurality of sensor pixels; and the second Sigma-Delta ADC receives a second respective charge of a second sensor pixel of the second plurality of sensor pixels.
  • the Sigma-Delta ADC receives a constant current.
  • the term“substantially” is used to describe element(s) or quantit(ies) ideally having an exact quality (e.g., fixed, the same, uniformed, equal, similar, proportional), but practically having qualities functionally equivalent to the exact quality.
  • an element or quantity is described as being substantially fixed or uniformed can deviate from the fixed or uniformed value, as long as the deviation is within a tolerance of the system (e.g., accuracy requirements, etc.).
  • two elements or quantities described as being substantially equal can be approximately equal, as long as the difference is within a tolerance that does not functionally affect a system’s operation.
  • a ratio is described as being one. However, it is understood that the ratio can be greater or less than one, as long as the ratio is within a tolerance of the system (e.g., accuracy requirements, etc.).

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Abstract

L'invention concerne des procédés de lecture et d'étalonnage de capteur et des circuits pour mettre en œuvre les procédés. Dans certains modes de réalisation, les procédés comprennent la commande d'un capteur actif à une tension. Dans certains modes de réalisation, les procédés comprennent l'utilisation d'un capteur d'étalonnage et les circuits comprennent le capteur d'étalonnage. Dans certains modes de réalisation, les procédés comprennent l'utilisation d'une source de courant d'étalonnage et les circuits comprennent la source de courant d'étalonnage. Dans certains modes de réalisation, un circuit de capteur comprend un CAN Sigma-Delta. Dans certains modes de réalisation, une colonne de capteurs est lue à l'aide d'un premier et d'un second circuit de lecture pendant une même période de ligne.
PCT/US2019/027982 2018-04-17 2019-04-17 Circuits de lecture et procédés WO2019204515A1 (fr)

Priority Applications (8)

Application Number Priority Date Filing Date Title
US17/048,046 US11555744B2 (en) 2018-04-17 2019-04-17 Readout circuits and methods
EP24179836.2A EP4403892A3 (fr) 2018-04-17 2019-04-17 Circuits et procédés de lecture
CN202410401813.5A CN118400626A (zh) 2018-04-17 2019-04-17 读出电路及方法
EP19721942.1A EP3782360B1 (fr) 2018-04-17 2019-04-17 Circuits de lecture et procédés
KR1020207032970A KR20200142575A (ko) 2018-04-17 2019-04-17 판독 회로들 및 방법들
CN201980031781.1A CN112106349B (zh) 2018-04-17 2019-04-17 读出电路及方法
JP2020557302A JP7289851B2 (ja) 2018-04-17 2019-04-17 読み出し回路および方法
US18/097,138 US20230236067A1 (en) 2018-04-17 2023-01-13 Readout circuits and methods

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US201862659048P 2018-04-17 2018-04-17
US62/659,048 2018-04-17
US201862757078P 2018-11-07 2018-11-07
US62/757,078 2018-11-07
US201962819376P 2019-03-15 2019-03-15
US62/819,376 2019-03-15

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US18/097,138 Continuation US20230236067A1 (en) 2018-04-17 2023-01-13 Readout circuits and methods

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EP (2) EP4403892A3 (fr)
JP (2) JP7289851B2 (fr)
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CN (2) CN112106349B (fr)
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